From 0ed23defed4e13a8485669279718de3f33f90ceb Mon Sep 17 00:00:00 2001
From: Asif Bashar <asif.bashar@gmail.com>
Date: Wed, 15 Oct 2025 22:08:58 -0700
Subject: [PATCH 01/24] PPL tostring() implementation issue #4492

Signed-off-by: Asif Bashar <asif.bashar@gmail.com>
---
 .../sql/calcite/utils/PPLOperandTypes.java    |   7 +
 .../function/PPLBuiltinOperators.java         |   2 +
 .../expression/function/PPLFuncImpTable.java  |   3 +
 .../function/udf/ToStringFunction.java        | 162 +++++++++++++++
 .../function/udf/ToStringFunctionTest.java    | 149 ++++++++++++++
 docs/user/ppl/functions/conversion.rst        |  92 +++++++++
 docs/user/ppl/functions/string.rst            |   3 +
 ppl/src/main/antlr/OpenSearchPPLLexer.g4      |   1 +
 ppl/src/main/antlr/OpenSearchPPLParser.g4     |   6 +-
 .../sql/ppl/parser/AstExpressionBuilder.java  |  11 +-
 .../calcite/CalcitePPLStringFunctionTest.java | 185 ++++++++++++++++++
 sql/src/main/antlr/OpenSearchSQLLexer.g4      |   1 +
 sql/src/main/antlr/OpenSearchSQLParser.g4     |   1 +
 13 files changed, 621 insertions(+), 2 deletions(-)
 create mode 100644 core/src/main/java/org/opensearch/sql/expression/function/udf/ToStringFunction.java
 create mode 100644 core/src/test/java/org/opensearch/sql/expression/function/udf/ToStringFunctionTest.java

diff --git a/core/src/main/java/org/opensearch/sql/calcite/utils/PPLOperandTypes.java b/core/src/main/java/org/opensearch/sql/calcite/utils/PPLOperandTypes.java
index 12a9a297542..69e1492538c 100644
--- a/core/src/main/java/org/opensearch/sql/calcite/utils/PPLOperandTypes.java
+++ b/core/src/main/java/org/opensearch/sql/calcite/utils/PPLOperandTypes.java
@@ -112,6 +112,13 @@ private PPLOperandTypes() {}
               SqlTypeFamily.INTEGER,
               SqlTypeFamily.INTEGER));
 
+  public static final UDFOperandMetadata BOOLEAN_OR_NUMERIC_STRING_OR_STRING_STRING =
+      UDFOperandMetadata.wrap(
+          (CompositeOperandTypeChecker)
+              OperandTypes.family(SqlTypeFamily.BOOLEAN)
+                  .or(OperandTypes.family(SqlTypeFamily.NUMERIC, SqlTypeFamily.STRING))
+                      .or(OperandTypes.family(SqlTypeFamily.STRING, SqlTypeFamily.STRING)));
+
   public static final UDFOperandMetadata NUMERIC_NUMERIC_OPTIONAL_NUMERIC =
       UDFOperandMetadata.wrap(
           (CompositeOperandTypeChecker)
diff --git a/core/src/main/java/org/opensearch/sql/expression/function/PPLBuiltinOperators.java b/core/src/main/java/org/opensearch/sql/expression/function/PPLBuiltinOperators.java
index 76f625ebd38..984f398b1ee 100644
--- a/core/src/main/java/org/opensearch/sql/expression/function/PPLBuiltinOperators.java
+++ b/core/src/main/java/org/opensearch/sql/expression/function/PPLBuiltinOperators.java
@@ -66,6 +66,7 @@
 import org.opensearch.sql.expression.function.udf.RexExtractMultiFunction;
 import org.opensearch.sql.expression.function.udf.RexOffsetFunction;
 import org.opensearch.sql.expression.function.udf.SpanFunction;
+import org.opensearch.sql.expression.function.udf.ToStringFunction;
 import org.opensearch.sql.expression.function.udf.condition.EarliestFunction;
 import org.opensearch.sql.expression.function.udf.condition.EnhancedCoalesceFunction;
 import org.opensearch.sql.expression.function.udf.condition.LatestFunction;
@@ -411,6 +412,7 @@ public class PPLBuiltinOperators extends ReflectiveSqlOperatorTable {
       RELEVANCE_QUERY_FUNCTION_INSTANCE.toUDF("multi_match", false);
   public static final SqlOperator NUMBER_TO_STRING =
       new NumberToStringFunction().toUDF("NUMBER_TO_STRING");
+  public static final SqlOperator TOSTRING = new ToStringFunction().toUDF("TOSTRING");
   public static final SqlOperator WIDTH_BUCKET =
       new org.opensearch.sql.expression.function.udf.binning.WidthBucketFunction()
           .toUDF("WIDTH_BUCKET");
diff --git a/core/src/main/java/org/opensearch/sql/expression/function/PPLFuncImpTable.java b/core/src/main/java/org/opensearch/sql/expression/function/PPLFuncImpTable.java
index 8297ecf73ce..de89df383d2 100644
--- a/core/src/main/java/org/opensearch/sql/expression/function/PPLFuncImpTable.java
+++ b/core/src/main/java/org/opensearch/sql/expression/function/PPLFuncImpTable.java
@@ -210,6 +210,7 @@
 import static org.opensearch.sql.expression.function.BuiltinFunctionName.TIMESTAMPDIFF;
 import static org.opensearch.sql.expression.function.BuiltinFunctionName.TIME_FORMAT;
 import static org.opensearch.sql.expression.function.BuiltinFunctionName.TIME_TO_SEC;
+import static org.opensearch.sql.expression.function.BuiltinFunctionName.TOSTRING;
 import static org.opensearch.sql.expression.function.BuiltinFunctionName.TO_DAYS;
 import static org.opensearch.sql.expression.function.BuiltinFunctionName.TO_SECONDS;
 import static org.opensearch.sql.expression.function.BuiltinFunctionName.TRANSFORM;
@@ -887,6 +888,7 @@ void populate() {
       registerOperator(WEEKOFYEAR, PPLBuiltinOperators.WEEK);
 
       registerOperator(INTERNAL_PATTERN_PARSER, PPLBuiltinOperators.PATTERN_PARSER);
+      registerOperator(TOSTRING, PPLBuiltinOperators.TOSTRING);
 
       // Register MVJOIN to use Calcite's ARRAY_JOIN
       register(
@@ -1058,6 +1060,7 @@ void populate() {
                               SqlTypeFamily.INTEGER,
                               SqlTypeFamily.INTEGER)),
               false));
+
       register(
           LOG,
           (FunctionImp2)
diff --git a/core/src/main/java/org/opensearch/sql/expression/function/udf/ToStringFunction.java b/core/src/main/java/org/opensearch/sql/expression/function/udf/ToStringFunction.java
new file mode 100644
index 00000000000..70d2a82b13c
--- /dev/null
+++ b/core/src/main/java/org/opensearch/sql/expression/function/udf/ToStringFunction.java
@@ -0,0 +1,162 @@
+/*
+ * Copyright OpenSearch Contributors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package org.opensearch.sql.expression.function.udf;
+
+import java.math.BigDecimal;
+import java.math.BigInteger;
+import java.text.NumberFormat;
+import java.time.Duration;
+import java.util.List;
+import java.util.Locale;
+import org.apache.calcite.adapter.enumerable.NotNullImplementor;
+import org.apache.calcite.adapter.enumerable.NullPolicy;
+import org.apache.calcite.adapter.enumerable.RexToLixTranslator;
+import org.apache.calcite.linq4j.function.Strict;
+import org.apache.calcite.linq4j.tree.Expression;
+import org.apache.calcite.linq4j.tree.Expressions;
+import org.apache.calcite.rex.RexCall;
+import org.apache.calcite.sql.type.SqlReturnTypeInference;
+import org.opensearch.sql.calcite.utils.PPLOperandTypes;
+import org.opensearch.sql.calcite.utils.PPLReturnTypes;
+import org.opensearch.sql.expression.function.ImplementorUDF;
+import org.opensearch.sql.expression.function.UDFOperandMetadata;
+
+/**
+ * A custom implementation of number/boolean to string .
+ *
+ * <p>This operator is necessary because tostring has following requirements "binary" Converts a
+ * number to a binary value. "hex" Converts the number to a hexadecimal value. "commas" Formats the
+ * number with commas. If the number includes a decimal, the function rounds the number to nearest
+ * two decimal places. "duration" Converts the value in seconds to the readable time format
+ * HH:MM:SS. if not format parameter provided, then consider value as boolean
+ */
+public class ToStringFunction extends ImplementorUDF {
+  public ToStringFunction() {
+    super(
+        new org.opensearch.sql.expression.function.udf.ToStringFunction.ToStringImplementor(),
+        NullPolicy.ANY);
+  }
+
+  public static final String DURATION_FORMAT = "duration";
+  public static final String HEX_FORMAT = "hex";
+  public static final String COMMAS_FORMAT = "commas";
+  public static final String BINARY_FORMAT = "binary";
+
+  @Override
+  public SqlReturnTypeInference getReturnTypeInference() {
+    return PPLReturnTypes.STRING_FORCE_NULLABLE;
+  }
+
+  @Override
+  public UDFOperandMetadata getOperandMetadata() {
+    return PPLOperandTypes.BOOLEAN_OR_NUMERIC_STRING_OR_STRING_STRING;
+  }
+
+  public static class ToStringImplementor implements NotNullImplementor {
+
+    @Override
+    public Expression implement(
+        RexToLixTranslator translator, RexCall call, List<Expression> translatedOperands) {
+      Expression fieldValue = translatedOperands.get(0);
+      if (translatedOperands.size() > 1) {
+        Expression format = translatedOperands.get(1);
+        return Expressions.call(ToStringFunction.class, "toString", fieldValue, format);
+      } else {
+        return Expressions.call(ToStringFunction.class, "toString", fieldValue);
+      }
+    }
+  }
+
+  @Strict
+  public static String toString(boolean fieldValue) {
+    if (fieldValue) {
+      return "True";
+    } else {
+      return "False";
+    }
+  }
+
+  @Strict
+  public static String toString(String fieldValue) {
+    return toString(Boolean.parseBoolean(fieldValue));
+  }
+
+  @Strict
+  public static String toString(BigDecimal num, String format) {
+    if (format.equals(DURATION_FORMAT)) {
+      Duration d = Duration.ofSeconds(num.toBigInteger().longValue());
+      long hours = d.toHours();
+      int minutes = d.toMinutesPart();
+      int remainingSeconds = d.toSecondsPart();
+
+      String time_str = String.format("%02d:%02d:%02d", hours, minutes, remainingSeconds);
+      return time_str;
+    } else if (format.equals(HEX_FORMAT)) {
+      return num.toBigInteger().toString(16);
+    } else if (format.equals(COMMAS_FORMAT)) {
+      NumberFormat nf = NumberFormat.getNumberInstance(Locale.getDefault());
+      nf.setMinimumFractionDigits(0);
+      nf.setMaximumFractionDigits(2);
+      return nf.format(num);
+
+    } else if (format.equals(BINARY_FORMAT)) {
+      BigInteger integerPart = num.toBigInteger(); // 42
+      return integerPart.toString(2);
+    }
+    return num.toString();
+  }
+
+  @Strict
+  public static String toString(double num, String format) {
+    if (format.equals(DURATION_FORMAT)) {
+      Duration d = Duration.ofSeconds(Math.round(num));
+      long hours = d.toHours();
+      int minutes = d.toMinutesPart();
+      int remainingSeconds = d.toSecondsPart();
+      String time_str = String.format("%02d:%02d:%02d", hours, minutes, remainingSeconds);
+      return time_str;
+    } else if (format.equals(HEX_FORMAT)) {
+      return Double.toHexString(num);
+    } else if (format.equals(COMMAS_FORMAT)) {
+      NumberFormat nf = NumberFormat.getNumberInstance(Locale.getDefault());
+      return nf.format(num);
+    } else if (format.equals(BINARY_FORMAT)) {
+      return Long.toBinaryString(Double.doubleToLongBits(num));
+    }
+    return Double.toString(num);
+  }
+
+  @Strict
+  public static String toString(int num, String format) {
+
+    if (format.equals(DURATION_FORMAT)) {
+
+      int hours = num / 3600;
+      int minutes = (num % 3600) / 60;
+      int seconds = num % 60;
+
+      String time_str = String.format("%02d:%02d:%02d", hours, minutes, seconds);
+      return time_str;
+    } else if (format.equals(HEX_FORMAT)) {
+      return Integer.toHexString(num);
+    } else if (format.equals(COMMAS_FORMAT)) {
+      NumberFormat nf = NumberFormat.getNumberInstance(Locale.getDefault());
+      return nf.format(num);
+    } else if (format.equals(BINARY_FORMAT)) {
+      return Integer.toBinaryString(num);
+    }
+    return Integer.toString(num);
+  }
+
+  @Strict
+  public static String toString(String str, String format) {
+    if (str.contains(".") || (str.length() > 10)) {
+      return toString(Double.parseDouble(str), format);
+    } else {
+      return toString(Integer.parseInt(str), format);
+    }
+  }
+}
diff --git a/core/src/test/java/org/opensearch/sql/expression/function/udf/ToStringFunctionTest.java b/core/src/test/java/org/opensearch/sql/expression/function/udf/ToStringFunctionTest.java
new file mode 100644
index 00000000000..cfd25796b23
--- /dev/null
+++ b/core/src/test/java/org/opensearch/sql/expression/function/udf/ToStringFunctionTest.java
@@ -0,0 +1,149 @@
+/*
+ * Copyright OpenSearch Contributors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package org.opensearch.sql.expression.function.udf;
+
+import org.junit.jupiter.api.Test;
+
+import java.math.BigDecimal;
+import java.util.Locale;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+public class ToStringFunctionTest {
+
+  private final ToStringFunction function = new ToStringFunction();
+
+    @Test
+    void testBooleanToString() {
+        assertEquals("True", ToStringFunction.toString(true));
+        assertEquals("False", ToStringFunction.toString(false));
+    }
+
+    @Test
+    void testStringBooleanToString() {
+        assertEquals("True", ToStringFunction.toString("true"));
+        assertEquals("False", ToStringFunction.toString("false"));
+        assertEquals("False", ToStringFunction.toString("anythingElse"));
+    }
+
+    @Test
+    void testBigDecimalToStringDurationFormat() {
+        BigDecimal num = new BigDecimal("3661"); // 1 hour 1 minute 1 second
+        String result = ToStringFunction.toString(num, ToStringFunction.DURATION_FORMAT);
+        assertEquals("01:01:01", result);
+    }
+
+    @Test
+    void testBigDecimalToStringHexFormat() {
+        BigDecimal num = new BigDecimal("255");
+        String result = ToStringFunction.toString(num, ToStringFunction.HEX_FORMAT);
+        assertEquals("ff", result);
+    }
+
+    @Test
+    void testBigDecimalToStringCommasFormat() {
+        Locale.setDefault(Locale.US); // Ensure predictable comma placement
+        BigDecimal num = new BigDecimal("1234567.891");
+        String result = ToStringFunction.toString(num, ToStringFunction.COMMAS_FORMAT);
+        assertTrue(result.contains(","));
+    }
+
+    @Test
+    void testBigDecimalToStringBinaryFormat() {
+        BigDecimal num = new BigDecimal("10");
+        String result = ToStringFunction.toString(num, ToStringFunction.BINARY_FORMAT);
+        assertEquals("1010", result);
+    }
+
+    @Test
+    void testBigDecimalToStringDefault() {
+        BigDecimal num = new BigDecimal("123.45");
+        assertEquals("123.45", ToStringFunction.toString(num, "unknown"));
+    }
+
+    @Test
+    void testDoubleToStringDurationFormat() {
+        double num = 3661.4;
+        String result = ToStringFunction.toString(num, ToStringFunction.DURATION_FORMAT);
+        assertEquals("01:01:01", result);
+    }
+
+    @Test
+    void testDoubleToStringHexFormat() {
+        double num = 10.5;
+        String result = ToStringFunction.toString(num, ToStringFunction.HEX_FORMAT);
+        assertTrue(result.startsWith("0x"));
+    }
+
+    @Test
+    void testDoubleToStringCommasFormat() {
+        Locale.setDefault(Locale.US);
+        double num = 12345.678;
+        String result = ToStringFunction.toString(num, ToStringFunction.COMMAS_FORMAT);
+        assertTrue(result.contains(","));
+    }
+
+    @Test
+    void testDoubleToStringBinaryFormat() {
+        double num = 10.0;
+        String result = ToStringFunction.toString(num, ToStringFunction.BINARY_FORMAT);
+        assertNotNull(result);
+        assertFalse(result.isEmpty());
+    }
+
+    @Test
+    void testDoubleToStringDefault() {
+        assertEquals("10.5", ToStringFunction.toString(10.5, "unknown"));
+    }
+
+    @Test
+    void testIntToStringDurationFormat() {
+        int num = 3661;
+        String result = ToStringFunction.toString(num, ToStringFunction.DURATION_FORMAT);
+        assertEquals("01:01:01", result);
+    }
+
+    @Test
+    void testIntToStringHexFormat() {
+        assertEquals("ff", ToStringFunction.toString(255, ToStringFunction.HEX_FORMAT));
+    }
+
+    @Test
+    void testIntToStringCommasFormat() {
+        Locale.setDefault(Locale.US);
+        String result = ToStringFunction.toString(1234567, ToStringFunction.COMMAS_FORMAT);
+        assertTrue(result.contains(","));
+    }
+
+    @Test
+    void testIntToStringBinaryFormat() {
+        assertEquals("1010", ToStringFunction.toString(10, ToStringFunction.BINARY_FORMAT));
+    }
+
+    @Test
+    void testIntToStringDefault() {
+        assertEquals("123", ToStringFunction.toString(123, "unknown"));
+    }
+
+    @Test
+    void testStringNumericToStringIntFormat() {
+        String result = ToStringFunction.toString("42", ToStringFunction.HEX_FORMAT);
+        assertEquals("2a", result);
+    }
+
+    @Test
+    void testStringNumericToStringDoubleFormat() {
+        String result = ToStringFunction.toString("42.5", ToStringFunction.COMMAS_FORMAT);
+        assertTrue(result.contains("42"));
+    }
+
+    @Test
+    void testStringLargeNumberAsDouble() {
+        String largeNum = "1234567890123";
+        String result = ToStringFunction.toString(largeNum, ToStringFunction.BINARY_FORMAT);
+        assertNotNull(result);
+    }
+}
diff --git a/docs/user/ppl/functions/conversion.rst b/docs/user/ppl/functions/conversion.rst
index dbe4403540c..21124c27edc 100644
--- a/docs/user/ppl/functions/conversion.rst
+++ b/docs/user/ppl/functions/conversion.rst
@@ -78,3 +78,95 @@ Cast function can be chained::
     |-------|
     | True  |
     +-------+
+
+TOSTRING
+-----
+
+Description
+>>>>>>>>>>>
+There are two available usage based on paraemter types and number of parameters.
+Usage with format type: tostring(number|string, string) converts the number in first argument  to provided format type string in second argument.
+         Return type: string
+Usage for boolean parameter without format type: tostring(boolean) converts the string to 'True' or 'False'.
+         Return type: string
+
+You can use this function with the eval commands and as part of eval expressions.
+The first  argument can be a number, number as string or boolean.
+If first  argument is a a number or number as string , second argument need to be format name.
+If first argument is boolean, then second argument is not needed.
+
+format types:
+a) "binary" Converts a number to a binary value.
+b) "hex" Converts the number to a hexadecimal value.
+c) "commas" Formats the number with commas. If the number includes a decimal, the function rounds the number to nearest two decimal places.
+d) "duration" Converts the value in seconds to the readable time format HH:MM:SS.
+The format argument is optional and is only used when the value argument is a number. The tostring function supports the following formats.
+
+Binary conversion
+You can use this function to convert a number to a string of its binary representation. For example, the result of the following function is 1001, because the binary representation of 9 is 1001.:
+eval result = tostring(9, "binary")
+
+For information about bitwise functions that you can use with the tostring function, see Bitwise functions.
+
+Basic examples
+The following example returns "True 0xF 12,345.68".
+... | eval n=tostring(1==1) + " " + tostring(15, "hex") + " " + tostring(12345.6789, "commas")
+The following example returns foo=615 and foo2=00:10:15. The 615 seconds is converted into minutes and seconds.
+
+... | eval foo=615 | eval foo2 = tostring(foo, "duration")
+The following example formats the column totalSales to display values with a currency symbol and commas. You must use a period between the currency value and the tostring function.
+
+Example::
+
+    os> source=people | eval `boolean_str` = tostring(1=1)| fields `boolean_str`
+    fetched rows / total rows = 1/1
+    +---------------------+
+    | boolean_str         |
+    |---------------------+
+    | True                |
+    +---------------------+
+    os> source=EMP |  eval salary_binary = tostring(SAL, "binary") | fields ENAME, salary_binary, SAL"
+    fetched rows / total rows = 1/1
+    +---------------+------------------+------------+
+    | ENAME         |   salary_binary  |  SAL       |
+    |---------------+------------------+------------+
+    | SMITH         | 1001110001000000 | 80000.00   |
+    +---------------+------------------+------------+
+    os> source=EMP |  eval salary_hex = tostring(SAL, "hex") | fields ENAME, salary_hex, SAL"
+    fetched rows / total rows = 1/1
+    +---------------+------------------+------------+
+    | ENAME         |   salary_hex  |  SAL          |
+    |---------------+------------------+------------+
+    | SMITH         |   13880       | 80000.00      |
+    +---------------+---------------+---------------+
+
+     os> source=EMP |  eval salary_commas = tostring(SAL, "commas") | fields ENAME, salary_commas, SAL"
+     fetched rows / total rows = 1/1
+    +---------------+------------------+------------+
+    | ENAME         |   salary_commas  |  SAL       |
+    |---------------+------------------+------------+
+    | SMITH         |   80,000         | 80000.00   |
+    +---------------+------------------+------------+
+
+
+        duration
+
+      os> source=EMP |  eval duration = tostring(6500, "duration") | fields ENAME, duration"
+          fetched rows / total rows = 1/1
+    +---------------+-------------+
+    | ENAME         |   duration  |
+    |---------------+-------------+
+    | SMITH         |   01:48:20  |
+    +---------------+-------------+
+
+Usage for boolean parameter without format type::
+
+Example::
+
+    os> source=people | eval `boolean_str` = tostring(1=1)| fields `boolean_str`
+    fetched rows / total rows = 1/1
+    +---------------------+
+    | boolean_str         |
+    |---------------------+
+    | True                |
+    +---------------------+
\ No newline at end of file
diff --git a/docs/user/ppl/functions/string.rst b/docs/user/ppl/functions/string.rst
index 24efa1434f5..43efed3c470 100644
--- a/docs/user/ppl/functions/string.rst
+++ b/docs/user/ppl/functions/string.rst
@@ -397,3 +397,6 @@ Example::
     |---------------------+---------------------|
     | HELLOWORLD          | HELLOWORLD          |
     +---------------------+---------------------+
+
+
+
diff --git a/ppl/src/main/antlr/OpenSearchPPLLexer.g4 b/ppl/src/main/antlr/OpenSearchPPLLexer.g4
index ba1e4960bb2..e528bb553ab 100644
--- a/ppl/src/main/antlr/OpenSearchPPLLexer.g4
+++ b/ppl/src/main/antlr/OpenSearchPPLLexer.g4
@@ -392,6 +392,7 @@ STRFTIME:                           'STRFTIME';
 // TEXT FUNCTIONS
 SUBSTR:                             'SUBSTR';
 SUBSTRING:                          'SUBSTRING';
+TOSTRING:                           'TOSTRING';
 LTRIM:                              'LTRIM';
 RTRIM:                              'RTRIM';
 TRIM:                               'TRIM';
diff --git a/ppl/src/main/antlr/OpenSearchPPLParser.g4 b/ppl/src/main/antlr/OpenSearchPPLParser.g4
index e13447b68e9..852c55c863c 100644
--- a/ppl/src/main/antlr/OpenSearchPPLParser.g4
+++ b/ppl/src/main/antlr/OpenSearchPPLParser.g4
@@ -847,11 +847,14 @@ evalFunctionCall
    : evalFunctionName LT_PRTHS functionArgs RT_PRTHS
    ;
 
-// cast function
+
+// cast, tostring function
 dataTypeFunctionCall
    : CAST LT_PRTHS logicalExpression AS convertedDataType RT_PRTHS
+   | TOSTRING LT_PRTHS functionArgs RT_PRTHS
    ;
 
+
 convertedDataType
    : typeName = DATE
    | typeName = TIME
@@ -1434,6 +1437,7 @@ searchableKeyWord
    | USING
    | VALUE
    | CAST
+   | TOSTRING
    | GET_FORMAT
    | EXTRACT
    | INTERVAL
diff --git a/ppl/src/main/java/org/opensearch/sql/ppl/parser/AstExpressionBuilder.java b/ppl/src/main/java/org/opensearch/sql/ppl/parser/AstExpressionBuilder.java
index f037376f5c2..1460a3efc9a 100644
--- a/ppl/src/main/java/org/opensearch/sql/ppl/parser/AstExpressionBuilder.java
+++ b/ppl/src/main/java/org/opensearch/sql/ppl/parser/AstExpressionBuilder.java
@@ -414,7 +414,16 @@ private Function buildFunction(
   /** Cast function. */
   @Override
   public UnresolvedExpression visitDataTypeFunctionCall(DataTypeFunctionCallContext ctx) {
-    return new Cast(visit(ctx.logicalExpression()), visit(ctx.convertedDataType()));
+    ParseTree rootNode = ctx.getChild(0);
+    String functionName = rootNode.getText();
+    final String mappedName =
+        FUNCTION_NAME_MAPPING.getOrDefault(functionName.toLowerCase(Locale.ROOT), functionName);
+
+    if (mappedName.equals("cast")) {
+      return new Cast(visit(ctx.logicalExpression()), visit(ctx.convertedDataType()));
+    } else {
+      return buildFunction(mappedName, ctx.functionArgs().functionArg());
+    }
   }
 
   @Override
diff --git a/ppl/src/test/java/org/opensearch/sql/ppl/calcite/CalcitePPLStringFunctionTest.java b/ppl/src/test/java/org/opensearch/sql/ppl/calcite/CalcitePPLStringFunctionTest.java
index 1e97052dea0..d41b2c22453 100644
--- a/ppl/src/test/java/org/opensearch/sql/ppl/calcite/CalcitePPLStringFunctionTest.java
+++ b/ppl/src/test/java/org/opensearch/sql/ppl/calcite/CalcitePPLStringFunctionTest.java
@@ -46,6 +46,191 @@ public void testLower() {
     verifyPPLToSparkSQL(root, expectedSparkSql);
   }
 
+  @Test
+  public void testToStringBoolean() {
+    String ppl = "source=EMP | eval boolean_value = tostring(1==1) | fields boolean_value |head 1";
+    RelNode root = getRelNode(ppl);
+    String expectedLogical =
+        "LogicalSort(fetch=[1])\n"
+            + "  LogicalProject(boolean_value=[TOSTRING(true)])\n"
+            + "    LogicalTableScan(table=[[scott, EMP]])\n";
+    String expectedResult = "boolean_value=True\n";
+    verifyLogical(root, expectedLogical);
+    verifyResult(root, expectedResult);
+
+    String expectedSparkSql =
+        "SELECT `TOSTRING`(TRUE) `boolean_value`\n" + "FROM `scott`.`EMP`\n" + "LIMIT 1";
+    verifyPPLToSparkSQL(root, expectedSparkSql);
+  }
+
+  @Test
+  public void testToStringBin() {
+    String ppl =
+        "source=EMP |  eval salary_binary = tostring(SAL, \"binary\") | fields ENAME,"
+            + " salary_binary, SAL";
+    RelNode root = getRelNode(ppl);
+    String expectedLogical =
+        "LogicalProject(ENAME=[$1], salary_binary=[TOSTRING($5, 'binary':VARCHAR)], SAL=[$5])\n"
+            + "  LogicalTableScan(table=[[scott, EMP]])\n";
+    String expectedResult =
+        "ENAME=SMITH; salary_binary=1100100000; SAL=800.00\n"
+            + "ENAME=ALLEN; salary_binary=11001000000; SAL=1600.00\n"
+            + "ENAME=WARD; salary_binary=10011100010; SAL=1250.00\n"
+            + "ENAME=JONES; salary_binary=101110011111; SAL=2975.00\n"
+            + "ENAME=MARTIN; salary_binary=10011100010; SAL=1250.00\n"
+            + "ENAME=BLAKE; salary_binary=101100100010; SAL=2850.00\n"
+            + "ENAME=CLARK; salary_binary=100110010010; SAL=2450.00\n"
+            + "ENAME=SCOTT; salary_binary=101110111000; SAL=3000.00\n"
+            + "ENAME=KING; salary_binary=1001110001000; SAL=5000.00\n"
+            + "ENAME=TURNER; salary_binary=10111011100; SAL=1500.00\n"
+            + "ENAME=ADAMS; salary_binary=10001001100; SAL=1100.00\n"
+            + "ENAME=JAMES; salary_binary=1110110110; SAL=950.00\n"
+            + "ENAME=FORD; salary_binary=101110111000; SAL=3000.00\n"
+            + "ENAME=MILLER; salary_binary=10100010100; SAL=1300.00\n";
+    verifyLogical(root, expectedLogical);
+    verifyResult(root, expectedResult);
+
+    String expectedSparkSql =
+        "SELECT `ENAME`, `TOSTRING`(`SAL`, 'binary') `salary_binary`, `SAL`\nFROM `scott`.`EMP`";
+    verifyPPLToSparkSQL(root, expectedSparkSql);
+  }
+
+  @Test
+  public void testToStringHex() {
+    String ppl =
+        "source=EMP |  eval salary_hex = tostring(SAL, \"hex\") | fields ENAME, salary_hex, SAL";
+    RelNode root = getRelNode(ppl);
+    String expectedLogical =
+        "LogicalProject(ENAME=[$1], salary_hex=[TOSTRING($5, 'hex':VARCHAR)], SAL=[$5])\n"
+            + "  LogicalTableScan(table=[[scott, EMP]])\n";
+    String expectedResult =
+        "ENAME=SMITH; salary_hex=320; SAL=800.00\n"
+            + "ENAME=ALLEN; salary_hex=640; SAL=1600.00\n"
+            + "ENAME=WARD; salary_hex=4e2; SAL=1250.00\n"
+            + "ENAME=JONES; salary_hex=b9f; SAL=2975.00\n"
+            + "ENAME=MARTIN; salary_hex=4e2; SAL=1250.00\n"
+            + "ENAME=BLAKE; salary_hex=b22; SAL=2850.00\n"
+            + "ENAME=CLARK; salary_hex=992; SAL=2450.00\n"
+            + "ENAME=SCOTT; salary_hex=bb8; SAL=3000.00\n"
+            + "ENAME=KING; salary_hex=1388; SAL=5000.00\n"
+            + "ENAME=TURNER; salary_hex=5dc; SAL=1500.00\n"
+            + "ENAME=ADAMS; salary_hex=44c; SAL=1100.00\n"
+            + "ENAME=JAMES; salary_hex=3b6; SAL=950.00\n"
+            + "ENAME=FORD; salary_hex=bb8; SAL=3000.00\n"
+            + "ENAME=MILLER; salary_hex=514; SAL=1300.00\n";
+    verifyLogical(root, expectedLogical);
+    verifyResult(root, expectedResult);
+
+    String expectedSparkSql =
+        "SELECT `ENAME`, `TOSTRING`(`SAL`, 'hex') `salary_hex`, `SAL`\nFROM `scott`.`EMP`";
+    verifyPPLToSparkSQL(root, expectedSparkSql);
+  }
+
+    @Test
+    public void testToStringHexFromNumberAsString() {
+        String ppl =
+                "source=EMP |  eval salary_hex = tostring(\"1600\", \"hex\") | fields ENAME, salary_hex| head 1";
+        RelNode root = getRelNode(ppl);
+        String expectedLogical =
+                "LogicalSort(fetch=[1])\n  LogicalProject(ENAME=[$1], salary_hex=[TOSTRING('1600':VARCHAR, 'hex':VARCHAR)])\n    LogicalTableScan(table=[[scott, EMP]])\n";
+        String expectedResult =
+                "ENAME=SMITH; salary_hex=640\n";
+        verifyLogical(root, expectedLogical);
+        verifyResult(root, expectedResult);
+
+        String expectedSparkSql =
+                "SELECT `ENAME`, `TOSTRING`('1600', 'hex') `salary_hex`\nFROM `scott`.`EMP`\nLIMIT 1";
+        verifyPPLToSparkSQL(root, expectedSparkSql);
+    }
+
+    @Test
+    public void testToStringCommaFromNumberAsString() {
+        String ppl =
+                "source=EMP |  eval salary_comma = tostring(\"160040222\", \"commas\") | fields ENAME, salary_comma| head 1";
+        RelNode root = getRelNode(ppl);
+        String expectedLogical =
+                "LogicalSort(fetch=[1])\n  LogicalProject(ENAME=[$1], salary_comma=[TOSTRING('160040222':VARCHAR, 'commas':VARCHAR)])\n    LogicalTableScan(table=[[scott, EMP]])\n";
+        String expectedResult =
+                "ENAME=SMITH; salary_comma=160,040,222\n";
+        verifyLogical(root, expectedLogical);
+        verifyResult(root, expectedResult);
+
+        String expectedSparkSql =
+                "SELECT `ENAME`, `TOSTRING`('160040222', 'commas') `salary_comma`\nFROM `scott`.`EMP`\nLIMIT 1";
+        verifyPPLToSparkSQL(root, expectedSparkSql);
+    }
+    @Test
+    public void testToStringBinaryFromNumberAsString() {
+        String ppl =
+                "source=EMP |  eval salary_binary = tostring(\"160040222\", \"binary\") | fields ENAME, salary_binary| head 1";
+        RelNode root = getRelNode(ppl);
+        String expectedLogical =
+                "LogicalSort(fetch=[1])\n  LogicalProject(ENAME=[$1], salary_binary=[TOSTRING('160040222':VARCHAR, 'binary':VARCHAR)])\n    LogicalTableScan(table=[[scott, EMP]])\n";
+        String expectedResult =
+                "ENAME=SMITH; salary_binary=1001100010100000010100011110\n";
+        verifyLogical(root, expectedLogical);
+        verifyResult(root, expectedResult);
+
+        String expectedSparkSql =
+                "SELECT `ENAME`, `TOSTRING`('160040222', 'binary') `salary_binary`\nFROM `scott`.`EMP`\nLIMIT 1";
+        verifyPPLToSparkSQL(root, expectedSparkSql);
+    }
+    @Test
+  public void testToStringCommas() {
+    String ppl =
+        "source=EMP |  eval salary_commas = tostring(SAL, \"commas\") | fields ENAME,"
+            + " salary_commas, SAL";
+    RelNode root = getRelNode(ppl);
+
+    String expectedLogical =
+        "LogicalProject(ENAME=[$1], salary_commas=[TOSTRING($5, 'commas':VARCHAR)], SAL=[$5])\n"
+            + "  LogicalTableScan(table=[[scott, EMP]])\n";
+    String expectedResult =
+        "ENAME=SMITH; salary_commas=800; SAL=800.00\n"
+            + "ENAME=ALLEN; salary_commas=1,600; SAL=1600.00\n"
+            + "ENAME=WARD; salary_commas=1,250; SAL=1250.00\n"
+            + "ENAME=JONES; salary_commas=2,975; SAL=2975.00\n"
+            + "ENAME=MARTIN; salary_commas=1,250; SAL=1250.00\n"
+            + "ENAME=BLAKE; salary_commas=2,850; SAL=2850.00\n"
+            + "ENAME=CLARK; salary_commas=2,450; SAL=2450.00\n"
+            + "ENAME=SCOTT; salary_commas=3,000; SAL=3000.00\n"
+            + "ENAME=KING; salary_commas=5,000; SAL=5000.00\n"
+            + "ENAME=TURNER; salary_commas=1,500; SAL=1500.00\n"
+            + "ENAME=ADAMS; salary_commas=1,100; SAL=1100.00\n"
+            + "ENAME=JAMES; salary_commas=950; SAL=950.00\n"
+            + "ENAME=FORD; salary_commas=3,000; SAL=3000.00\n"
+            + "ENAME=MILLER; salary_commas=1,300; SAL=1300.00\n";
+    verifyLogical(root, expectedLogical);
+    verifyResult(root, expectedResult);
+
+    String expectedSparkSql =
+        "SELECT `ENAME`, `TOSTRING`(`SAL`, 'commas') `salary_commas`, `SAL`\nFROM `scott`.`EMP`";
+    verifyPPLToSparkSQL(root, expectedSparkSql);
+  }
+
+  @Test
+  public void testToStringDuration() {
+    String ppl =
+        "source=EMP |  eval duration_commas = tostring(6500, \"duration\") | fields ENAME,"
+            + " duration_commas|HEAD 1";
+
+    RelNode root = getRelNode(ppl);
+
+    String expectedLogical =
+        "LogicalSort(fetch=[1])\n"
+            + "  LogicalProject(ENAME=[$1], duration_commas=[TOSTRING(6500, 'duration':VARCHAR)])\n"
+            + "    LogicalTableScan(table=[[scott, EMP]])\n";
+    String expectedResult = "ENAME=SMITH; duration_commas=01:48:20\n";
+    verifyLogical(root, expectedLogical);
+    verifyResult(root, expectedResult);
+
+    String expectedSparkSql =
+        "SELECT `ENAME`, `TOSTRING`(6500, 'duration') `duration_commas`\n"
+            + "FROM `scott`.`EMP`\n"
+            + "LIMIT 1";
+    verifyPPLToSparkSQL(root, expectedSparkSql);
+  }
+
   @Test
   public void testLike() {
     String ppl = "source=EMP | where like(JOB, 'SALE%') | stats count() as cnt";
diff --git a/sql/src/main/antlr/OpenSearchSQLLexer.g4 b/sql/src/main/antlr/OpenSearchSQLLexer.g4
index ba7c5be85ab..6465c692da3 100644
--- a/sql/src/main/antlr/OpenSearchSQLLexer.g4
+++ b/sql/src/main/antlr/OpenSearchSQLLexer.g4
@@ -133,6 +133,7 @@ STDDEV_SAMP:                        'STDDEV_SAMP';
 
 SUBSTRING:                          'SUBSTRING';
 TRIM:                               'TRIM';
+TOSTRING:                           'TOSTRING';
 
 // Keywords, but can be ID
 // Common Keywords, but can be ID
diff --git a/sql/src/main/antlr/OpenSearchSQLParser.g4 b/sql/src/main/antlr/OpenSearchSQLParser.g4
index 5f7361160b3..fbaef12fb98 100644
--- a/sql/src/main/antlr/OpenSearchSQLParser.g4
+++ b/sql/src/main/antlr/OpenSearchSQLParser.g4
@@ -417,6 +417,7 @@ specificFunction
    : CASE expression caseFuncAlternative+ (ELSE elseArg = functionArg)? END     # caseFunctionCall
    | CASE caseFuncAlternative+ (ELSE elseArg = functionArg)? END                # caseFunctionCall
    | CAST '(' expression AS convertedDataType ')'                               # dataTypeFunctionCall
+   | TOSTRING '(' functionArg  ')'                                              # dataTypeFunctionCall
    ;
 
 relevanceFunction

From 5a5b778cdf83230ff8a68a259a628e3ee0b3f318 Mon Sep 17 00:00:00 2001
From: Asif Bashar <asif.bashar@gmail.com>
Date: Thu, 16 Oct 2025 09:33:26 -0700
Subject: [PATCH 02/24] removed sql changes

Signed-off-by: Asif Bashar <asif.bashar@gmail.com>
---
 sql/src/main/antlr/OpenSearchSQLLexer.g4  | 1 -
 sql/src/main/antlr/OpenSearchSQLParser.g4 | 1 -
 2 files changed, 2 deletions(-)

diff --git a/sql/src/main/antlr/OpenSearchSQLLexer.g4 b/sql/src/main/antlr/OpenSearchSQLLexer.g4
index 6465c692da3..ba7c5be85ab 100644
--- a/sql/src/main/antlr/OpenSearchSQLLexer.g4
+++ b/sql/src/main/antlr/OpenSearchSQLLexer.g4
@@ -133,7 +133,6 @@ STDDEV_SAMP:                        'STDDEV_SAMP';
 
 SUBSTRING:                          'SUBSTRING';
 TRIM:                               'TRIM';
-TOSTRING:                           'TOSTRING';
 
 // Keywords, but can be ID
 // Common Keywords, but can be ID
diff --git a/sql/src/main/antlr/OpenSearchSQLParser.g4 b/sql/src/main/antlr/OpenSearchSQLParser.g4
index fbaef12fb98..5f7361160b3 100644
--- a/sql/src/main/antlr/OpenSearchSQLParser.g4
+++ b/sql/src/main/antlr/OpenSearchSQLParser.g4
@@ -417,7 +417,6 @@ specificFunction
    : CASE expression caseFuncAlternative+ (ELSE elseArg = functionArg)? END     # caseFunctionCall
    | CASE caseFuncAlternative+ (ELSE elseArg = functionArg)? END                # caseFunctionCall
    | CAST '(' expression AS convertedDataType ')'                               # dataTypeFunctionCall
-   | TOSTRING '(' functionArg  ')'                                              # dataTypeFunctionCall
    ;
 
 relevanceFunction

From 9d71a95f8487a7c5fa0e4cea8d11b4a3893efcaf Mon Sep 17 00:00:00 2001
From: Asif Bashar <asif.bashar@gmail.com>
Date: Thu, 16 Oct 2025 09:50:53 -0700
Subject: [PATCH 03/24] doc changes

Signed-off-by: Asif Bashar <asif.bashar@gmail.com>
---
 docs/user/ppl/functions/conversion.rst | 4 ++--
 docs/user/ppl/functions/string.rst     | 4 +---
 2 files changed, 3 insertions(+), 5 deletions(-)

diff --git a/docs/user/ppl/functions/conversion.rst b/docs/user/ppl/functions/conversion.rst
index 21124c27edc..33af0075431 100644
--- a/docs/user/ppl/functions/conversion.rst
+++ b/docs/user/ppl/functions/conversion.rst
@@ -95,14 +95,14 @@ The first  argument can be a number, number as string or boolean.
 If first  argument is a a number or number as string , second argument need to be format name.
 If first argument is boolean, then second argument is not needed.
 
-format types:
+Format types:
 a) "binary" Converts a number to a binary value.
 b) "hex" Converts the number to a hexadecimal value.
 c) "commas" Formats the number with commas. If the number includes a decimal, the function rounds the number to nearest two decimal places.
 d) "duration" Converts the value in seconds to the readable time format HH:MM:SS.
 The format argument is optional and is only used when the value argument is a number. The tostring function supports the following formats.
 
-Binary conversion
+Binary conversion:
 You can use this function to convert a number to a string of its binary representation. For example, the result of the following function is 1001, because the binary representation of 9 is 1001.:
 eval result = tostring(9, "binary")
 
diff --git a/docs/user/ppl/functions/string.rst b/docs/user/ppl/functions/string.rst
index 43efed3c470..c1dd52a5d89 100644
--- a/docs/user/ppl/functions/string.rst
+++ b/docs/user/ppl/functions/string.rst
@@ -397,6 +397,4 @@ Example::
     |---------------------+---------------------|
     | HELLOWORLD          | HELLOWORLD          |
     +---------------------+---------------------+
-
-
-
+    

From be2c2e264a8cc337940f3f1ae2152a15672ce2cb Mon Sep 17 00:00:00 2001
From: Asif Bashar <asif.bashar@gmail.com>
Date: Thu, 16 Oct 2025 09:52:09 -0700
Subject: [PATCH 04/24] docs changes

Signed-off-by: Asif Bashar <asif.bashar@gmail.com>
---
 docs/user/ppl/functions/conversion.rst | 12 ++++++------
 docs/user/ppl/functions/string.rst     |  3 +--
 2 files changed, 7 insertions(+), 8 deletions(-)

diff --git a/docs/user/ppl/functions/conversion.rst b/docs/user/ppl/functions/conversion.rst
index 33af0075431..9d0bf6eab1b 100644
--- a/docs/user/ppl/functions/conversion.rst
+++ b/docs/user/ppl/functions/conversion.rst
@@ -85,15 +85,15 @@ TOSTRING
 Description
 >>>>>>>>>>>
 There are two available usage based on paraemter types and number of parameters.
-Usage with format type: tostring(number|string, string) converts the number in first argument  to provided format type string in second argument.
-         Return type: string
+Usage with format type: tostring(ANY, [format]) converts the number in first argument  to provided format type string in second argument.
+   Return type: string
 Usage for boolean parameter without format type: tostring(boolean) converts the string to 'True' or 'False'.
-         Return type: string
+   Return type: string
 
 You can use this function with the eval commands and as part of eval expressions.
 The first  argument can be a number, number as string or boolean.
-If first  argument is a a number or number as string , second argument need to be format name.
-If first argument is boolean, then second argument is not needed.
+If first argument can be any valid type , second argument is optional and if provided , it needs to be format name.
+If first argument is boolean, then second argument is not used even if its provided.
 
 Format types:
 a) "binary" Converts a number to a binary value.
@@ -108,7 +108,7 @@ eval result = tostring(9, "binary")
 
 For information about bitwise functions that you can use with the tostring function, see Bitwise functions.
 
-Basic examples
+Basic examples:
 The following example returns "True 0xF 12,345.68".
 ... | eval n=tostring(1==1) + " " + tostring(15, "hex") + " " + tostring(12345.6789, "commas")
 The following example returns foo=615 and foo2=00:10:15. The 615 seconds is converted into minutes and seconds.
diff --git a/docs/user/ppl/functions/string.rst b/docs/user/ppl/functions/string.rst
index c1dd52a5d89..01b9b85b882 100644
--- a/docs/user/ppl/functions/string.rst
+++ b/docs/user/ppl/functions/string.rst
@@ -396,5 +396,4 @@ Example::
     | UPPER('helloworld') | UPPER('HELLOWORLD') |
     |---------------------+---------------------|
     | HELLOWORLD          | HELLOWORLD          |
-    +---------------------+---------------------+
-    
+    +---------------------+---------------------+
\ No newline at end of file

From fc763a431cbbdcad3fe35ab3f0e70f334d0b12a6 Mon Sep 17 00:00:00 2001
From: Asif Bashar <asif.bashar@gmail.com>
Date: Thu, 16 Oct 2025 10:00:16 -0700
Subject: [PATCH 05/24] reverted string doc changes

Signed-off-by: Asif Bashar <asif.bashar@gmail.com>
---
 docs/user/ppl/functions/string.rst | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/docs/user/ppl/functions/string.rst b/docs/user/ppl/functions/string.rst
index 01b9b85b882..24efa1434f5 100644
--- a/docs/user/ppl/functions/string.rst
+++ b/docs/user/ppl/functions/string.rst
@@ -396,4 +396,4 @@ Example::
     | UPPER('helloworld') | UPPER('HELLOWORLD') |
     |---------------------+---------------------|
     | HELLOWORLD          | HELLOWORLD          |
-    +---------------------+---------------------+
\ No newline at end of file
+    +---------------------+---------------------+

From a04eb14529029cf51d020e75ba5e7e6f921fb07c Mon Sep 17 00:00:00 2001
From: Asif Bashar <asif.bashar@gmail.com>
Date: Thu, 16 Oct 2025 10:06:46 -0700
Subject: [PATCH 06/24] removed extra word

Signed-off-by: Asif Bashar <asif.bashar@gmail.com>
---
 docs/user/ppl/functions/conversion.rst | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/docs/user/ppl/functions/conversion.rst b/docs/user/ppl/functions/conversion.rst
index 9d0bf6eab1b..58171d7cc72 100644
--- a/docs/user/ppl/functions/conversion.rst
+++ b/docs/user/ppl/functions/conversion.rst
@@ -91,7 +91,7 @@ Usage for boolean parameter without format type: tostring(boolean) converts the
    Return type: string
 
 You can use this function with the eval commands and as part of eval expressions.
-The first  argument can be a number, number as string or boolean.
+The first argument can be a number, number as string or boolean.
 If first argument can be any valid type , second argument is optional and if provided , it needs to be format name.
 If first argument is boolean, then second argument is not used even if its provided.
 
@@ -148,9 +148,6 @@ Example::
     | SMITH         |   80,000         | 80000.00   |
     +---------------+------------------+------------+
 
-
-        duration
-
       os> source=EMP |  eval duration = tostring(6500, "duration") | fields ENAME, duration"
           fetched rows / total rows = 1/1
     +---------------+-------------+

From 590a8e63add13b75fa90047cd2eca1ab4d802936 Mon Sep 17 00:00:00 2001
From: Asif Bashar <asif.bashar@gmail.com>
Date: Thu, 16 Oct 2025 10:24:25 -0700
Subject: [PATCH 07/24] added any type

Signed-off-by: Asif Bashar <asif.bashar@gmail.com>
---
 docs/user/ppl/functions/conversion.rst | 38 +++++++++++---------------
 1 file changed, 16 insertions(+), 22 deletions(-)

diff --git a/docs/user/ppl/functions/conversion.rst b/docs/user/ppl/functions/conversion.rst
index 58171d7cc72..c4ebe0505de 100644
--- a/docs/user/ppl/functions/conversion.rst
+++ b/docs/user/ppl/functions/conversion.rst
@@ -85,27 +85,22 @@ TOSTRING
 Description
 >>>>>>>>>>>
 There are two available usage based on paraemter types and number of parameters.
-Usage with format type: tostring(ANY, [format]) converts the number in first argument  to provided format type string in second argument.
+Usage with format type: tostring(ANY, [format]) converts the number in first argument  to provided format type string in second argument. If non number type, then it converts to default string representation.
    Return type: string
 Usage for boolean parameter without format type: tostring(boolean) converts the string to 'True' or 'False'.
    Return type: string
-
 You can use this function with the eval commands and as part of eval expressions.
-The first argument can be a number, number as string or boolean.
-If first argument can be any valid type , second argument is optional and if provided , it needs to be format name.
+
+If first argument can be any valid type , second argument is optional and if provided , it needs to be format name to convert to where first argument contains only numbers.
 If first argument is boolean, then second argument is not used even if its provided.
 
-Format types:
+Format types::
 a) "binary" Converts a number to a binary value.
 b) "hex" Converts the number to a hexadecimal value.
 c) "commas" Formats the number with commas. If the number includes a decimal, the function rounds the number to nearest two decimal places.
 d) "duration" Converts the value in seconds to the readable time format HH:MM:SS.
 The format argument is optional and is only used when the value argument is a number. The tostring function supports the following formats.
 
-Binary conversion:
-You can use this function to convert a number to a string of its binary representation. For example, the result of the following function is 1001, because the binary representation of 9 is 1001.:
-eval result = tostring(9, "binary")
-
 For information about bitwise functions that you can use with the tostring function, see Bitwise functions.
 
 Basic examples:
@@ -114,17 +109,11 @@ The following example returns "True 0xF 12,345.68".
 The following example returns foo=615 and foo2=00:10:15. The 615 seconds is converted into minutes and seconds.
 
 ... | eval foo=615 | eval foo2 = tostring(foo, "duration")
-The following example formats the column totalSales to display values with a currency symbol and commas. You must use a period between the currency value and the tostring function.
 
-Example::
 
-    os> source=people | eval `boolean_str` = tostring(1=1)| fields `boolean_str`
-    fetched rows / total rows = 1/1
-    +---------------------+
-    | boolean_str         |
-    |---------------------+
-    | True                |
-    +---------------------+
+
+You can use this function to convert a number to a string of its binary representation.
+Example::
     os> source=EMP |  eval salary_binary = tostring(SAL, "binary") | fields ENAME, salary_binary, SAL"
     fetched rows / total rows = 1/1
     +---------------+------------------+------------+
@@ -132,6 +121,10 @@ Example::
     |---------------+------------------+------------+
     | SMITH         | 1001110001000000 | 80000.00   |
     +---------------+------------------+------------+
+
+
+You can use this function to convert a number to a string of its hex representation.
+Example::
     os> source=EMP |  eval salary_hex = tostring(SAL, "hex") | fields ENAME, salary_hex, SAL"
     fetched rows / total rows = 1/1
     +---------------+------------------+------------+
@@ -140,6 +133,8 @@ Example::
     | SMITH         |   13880       | 80000.00      |
     +---------------+---------------+---------------+
 
+The following example formats the column totalSales to display values  with commas.
+Example::
      os> source=EMP |  eval salary_commas = tostring(SAL, "commas") | fields ENAME, salary_commas, SAL"
      fetched rows / total rows = 1/1
     +---------------+------------------+------------+
@@ -147,7 +142,8 @@ Example::
     |---------------+------------------+------------+
     | SMITH         |   80,000         | 80000.00   |
     +---------------+------------------+------------+
-
+The following example converts number of seconds to HH:MM:SS format representing hours, minutes and seconds.
+Example::
       os> source=EMP |  eval duration = tostring(6500, "duration") | fields ENAME, duration"
           fetched rows / total rows = 1/1
     +---------------+-------------+
@@ -156,10 +152,8 @@ Example::
     | SMITH         |   01:48:20  |
     +---------------+-------------+
 
-Usage for boolean parameter without format type::
-
+Example for boolean parameter.
 Example::
-
     os> source=people | eval `boolean_str` = tostring(1=1)| fields `boolean_str`
     fetched rows / total rows = 1/1
     +---------------------+

From 6938e2c08dfef04119f1e37802d0a3a9554a0d21 Mon Sep 17 00:00:00 2001
From: Asif Bashar <asif.bashar@gmail.com>
Date: Thu, 16 Oct 2025 11:00:43 -0700
Subject: [PATCH 08/24] doc formatting fixes

Signed-off-by: Asif Bashar <asif.bashar@gmail.com>
---
 docs/user/ppl/functions/conversion.rst | 38 ++++++++++++++++----------
 1 file changed, 24 insertions(+), 14 deletions(-)

diff --git a/docs/user/ppl/functions/conversion.rst b/docs/user/ppl/functions/conversion.rst
index c4ebe0505de..280befee0aa 100644
--- a/docs/user/ppl/functions/conversion.rst
+++ b/docs/user/ppl/functions/conversion.rst
@@ -80,40 +80,44 @@ Cast function can be chained::
     +-------+
 
 TOSTRING
------
+-----------
 
 Description
 >>>>>>>>>>>
-There are two available usage based on paraemter types and number of parameters.
-Usage with format type: tostring(ANY, [format]) converts the number in first argument  to provided format type string in second argument. If non number type, then it converts to default string representation.
-   Return type: string
-Usage for boolean parameter without format type: tostring(boolean) converts the string to 'True' or 'False'.
-   Return type: string
-You can use this function with the eval commands and as part of eval expressions.
+The following usage options are available, depending on the parameter types and the number of parameters.
 
-If first argument can be any valid type , second argument is optional and if provided , it needs to be format name to convert to where first argument contains only numbers.
-If first argument is boolean, then second argument is not used even if its provided.
+Usage with format type: tostring(ANY, [format]): Converts the number in first argument  to provided format type string in second argument. If non number type, then it converts to default string representation.
+Return type: string
+
+Usage for boolean parameter without format type tostring(boolean): Converts the string to 'True' or 'False'.
+Return type: string
+
+You can use this function with the eval commands and as part of eval expressions. If first argument can be any valid type , second argument is optional and if provided , it needs to be format name to convert to where first argument contains only numbers. If first argument is boolean, then second argument is not used even if its provided.
+
+Format types:
 
-Format types::
 a) "binary" Converts a number to a binary value.
 b) "hex" Converts the number to a hexadecimal value.
 c) "commas" Formats the number with commas. If the number includes a decimal, the function rounds the number to nearest two decimal places.
 d) "duration" Converts the value in seconds to the readable time format HH:MM:SS.
-The format argument is optional and is only used when the value argument is a number. The tostring function supports the following formats.
 
-For information about bitwise functions that you can use with the tostring function, see Bitwise functions.
+The format argument is optional and is only used when the value argument is a number. The tostring function supports the following formats.
 
 Basic examples:
+
 The following example returns "True 0xF 12,345.68".
-... | eval n=tostring(1==1) + " " + tostring(15, "hex") + " " + tostring(12345.6789, "commas")
+
+    ... | eval n=tostring(1==1) + " " + tostring(15, "hex") + " " + tostring(12345.6789, "commas")
+
 The following example returns foo=615 and foo2=00:10:15. The 615 seconds is converted into minutes and seconds.
 
-... | eval foo=615 | eval foo2 = tostring(foo, "duration")
+    ... | eval foo=615 | eval foo2 = tostring(foo, "duration")
 
 
 
 You can use this function to convert a number to a string of its binary representation.
 Example::
+
     os> source=EMP |  eval salary_binary = tostring(SAL, "binary") | fields ENAME, salary_binary, SAL"
     fetched rows / total rows = 1/1
     +---------------+------------------+------------+
@@ -125,6 +129,7 @@ Example::
 
 You can use this function to convert a number to a string of its hex representation.
 Example::
+
     os> source=EMP |  eval salary_hex = tostring(SAL, "hex") | fields ENAME, salary_hex, SAL"
     fetched rows / total rows = 1/1
     +---------------+------------------+------------+
@@ -135,6 +140,7 @@ Example::
 
 The following example formats the column totalSales to display values  with commas.
 Example::
+
      os> source=EMP |  eval salary_commas = tostring(SAL, "commas") | fields ENAME, salary_commas, SAL"
      fetched rows / total rows = 1/1
     +---------------+------------------+------------+
@@ -142,8 +148,10 @@ Example::
     |---------------+------------------+------------+
     | SMITH         |   80,000         | 80000.00   |
     +---------------+------------------+------------+
+
 The following example converts number of seconds to HH:MM:SS format representing hours, minutes and seconds.
 Example::
+
       os> source=EMP |  eval duration = tostring(6500, "duration") | fields ENAME, duration"
           fetched rows / total rows = 1/1
     +---------------+-------------+
@@ -154,8 +162,10 @@ Example::
 
 Example for boolean parameter.
 Example::
+
     os> source=people | eval `boolean_str` = tostring(1=1)| fields `boolean_str`
     fetched rows / total rows = 1/1
+
     +---------------------+
     | boolean_str         |
     |---------------------+

From 314fccdaee8ab28ede0eab2f1da4e2b83cc24e96 Mon Sep 17 00:00:00 2001
From: Asif Bashar <asif.bashar@gmail.com>
Date: Thu, 16 Oct 2025 11:04:06 -0700
Subject: [PATCH 09/24] description for boolean example

Signed-off-by: Asif Bashar <asif.bashar@gmail.com>
---
 docs/user/ppl/functions/conversion.rst | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/docs/user/ppl/functions/conversion.rst b/docs/user/ppl/functions/conversion.rst
index 280befee0aa..036a89daf00 100644
--- a/docs/user/ppl/functions/conversion.rst
+++ b/docs/user/ppl/functions/conversion.rst
@@ -160,7 +160,7 @@ Example::
     | SMITH         |   01:48:20  |
     +---------------+-------------+
 
-Example for boolean parameter.
+The following example for converts boolean parameter to string.
 Example::
 
     os> source=people | eval `boolean_str` = tostring(1=1)| fields `boolean_str`

From 0ee17b9a4a262a1d6070b98ae8a1162f6556f517 Mon Sep 17 00:00:00 2001
From: Asif Bashar <asif.bashar@gmail.com>
Date: Fri, 17 Oct 2025 13:21:49 -0700
Subject: [PATCH 10/24] added format_time call from calcite , added
 duration_millis as splunk default duration is in seconds which will be used
 for duration format , added cast call for tostring with 1 argument

Signed-off-by: Asif Bashar <asif.bashar@gmail.com>
---
 .../sql/calcite/utils/PPLOperandTypes.java    |   2 +-
 .../function/udf/ToStringFunction.java        |  53 ++--
 .../function/udf/ToStringFunctionTest.java    | 265 +++++++++---------
 .../sql/ppl/parser/AstExpressionBuilder.java  |  52 +++-
 .../calcite/CalcitePPLStringFunctionTest.java | 157 +++++++----
 5 files changed, 312 insertions(+), 217 deletions(-)

diff --git a/core/src/main/java/org/opensearch/sql/calcite/utils/PPLOperandTypes.java b/core/src/main/java/org/opensearch/sql/calcite/utils/PPLOperandTypes.java
index 69e1492538c..20811f1af48 100644
--- a/core/src/main/java/org/opensearch/sql/calcite/utils/PPLOperandTypes.java
+++ b/core/src/main/java/org/opensearch/sql/calcite/utils/PPLOperandTypes.java
@@ -117,7 +117,7 @@ private PPLOperandTypes() {}
           (CompositeOperandTypeChecker)
               OperandTypes.family(SqlTypeFamily.BOOLEAN)
                   .or(OperandTypes.family(SqlTypeFamily.NUMERIC, SqlTypeFamily.STRING))
-                      .or(OperandTypes.family(SqlTypeFamily.STRING, SqlTypeFamily.STRING)));
+                  .or(OperandTypes.family(SqlTypeFamily.STRING, SqlTypeFamily.STRING)));
 
   public static final UDFOperandMetadata NUMERIC_NUMERIC_OPTIONAL_NUMERIC =
       UDFOperandMetadata.wrap(
diff --git a/core/src/main/java/org/opensearch/sql/expression/function/udf/ToStringFunction.java b/core/src/main/java/org/opensearch/sql/expression/function/udf/ToStringFunction.java
index 70d2a82b13c..be76100f38d 100644
--- a/core/src/main/java/org/opensearch/sql/expression/function/udf/ToStringFunction.java
+++ b/core/src/main/java/org/opensearch/sql/expression/function/udf/ToStringFunction.java
@@ -8,7 +8,6 @@
 import java.math.BigDecimal;
 import java.math.BigInteger;
 import java.text.NumberFormat;
-import java.time.Duration;
 import java.util.List;
 import java.util.Locale;
 import org.apache.calcite.adapter.enumerable.NotNullImplementor;
@@ -18,6 +17,7 @@
 import org.apache.calcite.linq4j.tree.Expression;
 import org.apache.calcite.linq4j.tree.Expressions;
 import org.apache.calcite.rex.RexCall;
+import org.apache.calcite.runtime.SqlFunctions;
 import org.apache.calcite.sql.type.SqlReturnTypeInference;
 import org.opensearch.sql.calcite.utils.PPLOperandTypes;
 import org.opensearch.sql.calcite.utils.PPLReturnTypes;
@@ -41,9 +41,13 @@ public ToStringFunction() {
   }
 
   public static final String DURATION_FORMAT = "duration";
+  public static final String DURATION_MILLIS_FORMAT = "duration_millis";
   public static final String HEX_FORMAT = "hex";
   public static final String COMMAS_FORMAT = "commas";
   public static final String BINARY_FORMAT = "binary";
+  public static final SqlFunctions.DateFormatFunction dateTimeFormatter =
+      new SqlFunctions.DateFormatFunction();
+  public static final String format24hour = "%H:%M:%S"; // 24-hour format
 
   @Override
   public SqlReturnTypeInference getReturnTypeInference() {
@@ -65,7 +69,13 @@ public Expression implement(
         Expression format = translatedOperands.get(1);
         return Expressions.call(ToStringFunction.class, "toString", fieldValue, format);
       } else {
-        return Expressions.call(ToStringFunction.class, "toString", fieldValue);
+        // autoboxes to Boolean
+
+        if (!fieldValue.getType().getTypeName().equals("Boolean")) {
+          return Expressions.call(ToStringFunction.class, "toString", fieldValue);
+        } else {
+          return Expressions.call(ToStringFunction.class, "toString", fieldValue);
+        }
       }
     }
   }
@@ -87,13 +97,13 @@ public static String toString(String fieldValue) {
   @Strict
   public static String toString(BigDecimal num, String format) {
     if (format.equals(DURATION_FORMAT)) {
-      Duration d = Duration.ofSeconds(num.toBigInteger().longValue());
-      long hours = d.toHours();
-      int minutes = d.toMinutesPart();
-      int remainingSeconds = d.toSecondsPart();
 
-      String time_str = String.format("%02d:%02d:%02d", hours, minutes, remainingSeconds);
-      return time_str;
+      return dateTimeFormatter.formatTime(format24hour, num.toBigInteger().intValue() * 1000);
+
+    } else if (format.equals(DURATION_MILLIS_FORMAT)) {
+
+      return dateTimeFormatter.formatTime(format24hour, num.toBigInteger().intValue());
+
     } else if (format.equals(HEX_FORMAT)) {
       return num.toBigInteger().toString(16);
     } else if (format.equals(COMMAS_FORMAT)) {
@@ -112,12 +122,11 @@ public static String toString(BigDecimal num, String format) {
   @Strict
   public static String toString(double num, String format) {
     if (format.equals(DURATION_FORMAT)) {
-      Duration d = Duration.ofSeconds(Math.round(num));
-      long hours = d.toHours();
-      int minutes = d.toMinutesPart();
-      int remainingSeconds = d.toSecondsPart();
-      String time_str = String.format("%02d:%02d:%02d", hours, minutes, remainingSeconds);
-      return time_str;
+      return dateTimeFormatter.formatTime(format24hour, ((int) Math.round(num)) * 1000);
+    } else if (format.equals(DURATION_MILLIS_FORMAT)) {
+
+      return dateTimeFormatter.formatTime(format24hour, ((int) Math.round(num)));
+
     } else if (format.equals(HEX_FORMAT)) {
       return Double.toHexString(num);
     } else if (format.equals(COMMAS_FORMAT)) {
@@ -129,17 +138,19 @@ public static String toString(double num, String format) {
     return Double.toString(num);
   }
 
+  @Strict
+  public static String toString(short num, String format) {
+    int i = (int) num;
+    return toString(i, format);
+  }
+
   @Strict
   public static String toString(int num, String format) {
 
     if (format.equals(DURATION_FORMAT)) {
-
-      int hours = num / 3600;
-      int minutes = (num % 3600) / 60;
-      int seconds = num % 60;
-
-      String time_str = String.format("%02d:%02d:%02d", hours, minutes, seconds);
-      return time_str;
+      return dateTimeFormatter.formatTime(format24hour, num * 1000);
+    } else if (format.equals(DURATION_MILLIS_FORMAT)) {
+      return dateTimeFormatter.formatTime(format24hour, num);
     } else if (format.equals(HEX_FORMAT)) {
       return Integer.toHexString(num);
     } else if (format.equals(COMMAS_FORMAT)) {
diff --git a/core/src/test/java/org/opensearch/sql/expression/function/udf/ToStringFunctionTest.java b/core/src/test/java/org/opensearch/sql/expression/function/udf/ToStringFunctionTest.java
index cfd25796b23..f0867f93327 100644
--- a/core/src/test/java/org/opensearch/sql/expression/function/udf/ToStringFunctionTest.java
+++ b/core/src/test/java/org/opensearch/sql/expression/function/udf/ToStringFunctionTest.java
@@ -5,145 +5,144 @@
 
 package org.opensearch.sql.expression.function.udf;
 
-import org.junit.jupiter.api.Test;
+import static org.junit.jupiter.api.Assertions.*;
 
 import java.math.BigDecimal;
 import java.util.Locale;
-
-import static org.junit.jupiter.api.Assertions.*;
+import org.junit.jupiter.api.Test;
 
 public class ToStringFunctionTest {
 
   private final ToStringFunction function = new ToStringFunction();
 
-    @Test
-    void testBooleanToString() {
-        assertEquals("True", ToStringFunction.toString(true));
-        assertEquals("False", ToStringFunction.toString(false));
-    }
-
-    @Test
-    void testStringBooleanToString() {
-        assertEquals("True", ToStringFunction.toString("true"));
-        assertEquals("False", ToStringFunction.toString("false"));
-        assertEquals("False", ToStringFunction.toString("anythingElse"));
-    }
-
-    @Test
-    void testBigDecimalToStringDurationFormat() {
-        BigDecimal num = new BigDecimal("3661"); // 1 hour 1 minute 1 second
-        String result = ToStringFunction.toString(num, ToStringFunction.DURATION_FORMAT);
-        assertEquals("01:01:01", result);
-    }
-
-    @Test
-    void testBigDecimalToStringHexFormat() {
-        BigDecimal num = new BigDecimal("255");
-        String result = ToStringFunction.toString(num, ToStringFunction.HEX_FORMAT);
-        assertEquals("ff", result);
-    }
-
-    @Test
-    void testBigDecimalToStringCommasFormat() {
-        Locale.setDefault(Locale.US); // Ensure predictable comma placement
-        BigDecimal num = new BigDecimal("1234567.891");
-        String result = ToStringFunction.toString(num, ToStringFunction.COMMAS_FORMAT);
-        assertTrue(result.contains(","));
-    }
-
-    @Test
-    void testBigDecimalToStringBinaryFormat() {
-        BigDecimal num = new BigDecimal("10");
-        String result = ToStringFunction.toString(num, ToStringFunction.BINARY_FORMAT);
-        assertEquals("1010", result);
-    }
-
-    @Test
-    void testBigDecimalToStringDefault() {
-        BigDecimal num = new BigDecimal("123.45");
-        assertEquals("123.45", ToStringFunction.toString(num, "unknown"));
-    }
-
-    @Test
-    void testDoubleToStringDurationFormat() {
-        double num = 3661.4;
-        String result = ToStringFunction.toString(num, ToStringFunction.DURATION_FORMAT);
-        assertEquals("01:01:01", result);
-    }
-
-    @Test
-    void testDoubleToStringHexFormat() {
-        double num = 10.5;
-        String result = ToStringFunction.toString(num, ToStringFunction.HEX_FORMAT);
-        assertTrue(result.startsWith("0x"));
-    }
-
-    @Test
-    void testDoubleToStringCommasFormat() {
-        Locale.setDefault(Locale.US);
-        double num = 12345.678;
-        String result = ToStringFunction.toString(num, ToStringFunction.COMMAS_FORMAT);
-        assertTrue(result.contains(","));
-    }
-
-    @Test
-    void testDoubleToStringBinaryFormat() {
-        double num = 10.0;
-        String result = ToStringFunction.toString(num, ToStringFunction.BINARY_FORMAT);
-        assertNotNull(result);
-        assertFalse(result.isEmpty());
-    }
-
-    @Test
-    void testDoubleToStringDefault() {
-        assertEquals("10.5", ToStringFunction.toString(10.5, "unknown"));
-    }
-
-    @Test
-    void testIntToStringDurationFormat() {
-        int num = 3661;
-        String result = ToStringFunction.toString(num, ToStringFunction.DURATION_FORMAT);
-        assertEquals("01:01:01", result);
-    }
-
-    @Test
-    void testIntToStringHexFormat() {
-        assertEquals("ff", ToStringFunction.toString(255, ToStringFunction.HEX_FORMAT));
-    }
-
-    @Test
-    void testIntToStringCommasFormat() {
-        Locale.setDefault(Locale.US);
-        String result = ToStringFunction.toString(1234567, ToStringFunction.COMMAS_FORMAT);
-        assertTrue(result.contains(","));
-    }
-
-    @Test
-    void testIntToStringBinaryFormat() {
-        assertEquals("1010", ToStringFunction.toString(10, ToStringFunction.BINARY_FORMAT));
-    }
-
-    @Test
-    void testIntToStringDefault() {
-        assertEquals("123", ToStringFunction.toString(123, "unknown"));
-    }
-
-    @Test
-    void testStringNumericToStringIntFormat() {
-        String result = ToStringFunction.toString("42", ToStringFunction.HEX_FORMAT);
-        assertEquals("2a", result);
-    }
-
-    @Test
-    void testStringNumericToStringDoubleFormat() {
-        String result = ToStringFunction.toString("42.5", ToStringFunction.COMMAS_FORMAT);
-        assertTrue(result.contains("42"));
-    }
-
-    @Test
-    void testStringLargeNumberAsDouble() {
-        String largeNum = "1234567890123";
-        String result = ToStringFunction.toString(largeNum, ToStringFunction.BINARY_FORMAT);
-        assertNotNull(result);
-    }
+  @Test
+  void testBooleanToString() {
+    assertEquals("True", ToStringFunction.toString(true));
+    assertEquals("False", ToStringFunction.toString(false));
+  }
+
+  @Test
+  void testStringBooleanToString() {
+    assertEquals("True", ToStringFunction.toString("true"));
+    assertEquals("False", ToStringFunction.toString("false"));
+    assertEquals("False", ToStringFunction.toString("anythingElse"));
+  }
+
+  @Test
+  void testBigDecimalToStringDurationFormat() {
+    BigDecimal num = new BigDecimal("3661"); // 1 hour 1 minute 1 second
+    String result = ToStringFunction.toString(num, ToStringFunction.DURATION_FORMAT);
+    assertEquals("01:01:01", result);
+  }
+
+  @Test
+  void testBigDecimalToStringHexFormat() {
+    BigDecimal num = new BigDecimal("255");
+    String result = ToStringFunction.toString(num, ToStringFunction.HEX_FORMAT);
+    assertEquals("ff", result);
+  }
+
+  @Test
+  void testBigDecimalToStringCommasFormat() {
+    Locale.setDefault(Locale.US); // Ensure predictable comma placement
+    BigDecimal num = new BigDecimal("1234567.891");
+    String result = ToStringFunction.toString(num, ToStringFunction.COMMAS_FORMAT);
+    assertTrue(result.contains(","));
+  }
+
+  @Test
+  void testBigDecimalToStringBinaryFormat() {
+    BigDecimal num = new BigDecimal("10");
+    String result = ToStringFunction.toString(num, ToStringFunction.BINARY_FORMAT);
+    assertEquals("1010", result);
+  }
+
+  @Test
+  void testBigDecimalToStringDefault() {
+    BigDecimal num = new BigDecimal("123.45");
+    assertEquals("123.45", ToStringFunction.toString(num, "unknown"));
+  }
+
+  @Test
+  void testDoubleToStringDurationFormat() {
+    double num = 3661.4;
+    String result = ToStringFunction.toString(num, ToStringFunction.DURATION_FORMAT);
+    assertEquals("01:01:01", result);
+  }
+
+  @Test
+  void testDoubleToStringHexFormat() {
+    double num = 10.5;
+    String result = ToStringFunction.toString(num, ToStringFunction.HEX_FORMAT);
+    assertTrue(result.startsWith("0x"));
+  }
+
+  @Test
+  void testDoubleToStringCommasFormat() {
+    Locale.setDefault(Locale.US);
+    double num = 12345.678;
+    String result = ToStringFunction.toString(num, ToStringFunction.COMMAS_FORMAT);
+    assertTrue(result.contains(","));
+  }
+
+  @Test
+  void testDoubleToStringBinaryFormat() {
+    double num = 10.0;
+    String result = ToStringFunction.toString(num, ToStringFunction.BINARY_FORMAT);
+    assertNotNull(result);
+    assertFalse(result.isEmpty());
+  }
+
+  @Test
+  void testDoubleToStringDefault() {
+    assertEquals("10.5", ToStringFunction.toString(10.5, "unknown"));
+  }
+
+  @Test
+  void testIntToStringDurationFormat() {
+    int num = 3661;
+    String result = ToStringFunction.toString(num, ToStringFunction.DURATION_FORMAT);
+    assertEquals("01:01:01", result);
+  }
+
+  @Test
+  void testIntToStringHexFormat() {
+    assertEquals("ff", ToStringFunction.toString(255, ToStringFunction.HEX_FORMAT));
+  }
+
+  @Test
+  void testIntToStringCommasFormat() {
+    Locale.setDefault(Locale.US);
+    String result = ToStringFunction.toString(1234567, ToStringFunction.COMMAS_FORMAT);
+    assertTrue(result.contains(","));
+  }
+
+  @Test
+  void testIntToStringBinaryFormat() {
+    assertEquals("1010", ToStringFunction.toString(10, ToStringFunction.BINARY_FORMAT));
+  }
+
+  @Test
+  void testIntToStringDefault() {
+    assertEquals("123", ToStringFunction.toString(123, "unknown"));
+  }
+
+  @Test
+  void testStringNumericToStringIntFormat() {
+    String result = ToStringFunction.toString("42", ToStringFunction.HEX_FORMAT);
+    assertEquals("2a", result);
+  }
+
+  @Test
+  void testStringNumericToStringDoubleFormat() {
+    String result = ToStringFunction.toString("42.5", ToStringFunction.COMMAS_FORMAT);
+    assertTrue(result.contains("42"));
+  }
+
+  @Test
+  void testStringLargeNumberAsDouble() {
+    String largeNum = "1234567890123";
+    String result = ToStringFunction.toString(largeNum, ToStringFunction.BINARY_FORMAT);
+    assertNotNull(result);
+  }
 }
diff --git a/ppl/src/main/java/org/opensearch/sql/ppl/parser/AstExpressionBuilder.java b/ppl/src/main/java/org/opensearch/sql/ppl/parser/AstExpressionBuilder.java
index 1460a3efc9a..2112282f728 100644
--- a/ppl/src/main/java/org/opensearch/sql/ppl/parser/AstExpressionBuilder.java
+++ b/ppl/src/main/java/org/opensearch/sql/ppl/parser/AstExpressionBuilder.java
@@ -19,6 +19,7 @@
 import java.util.stream.Collectors;
 import java.util.stream.IntStream;
 import java.util.stream.Stream;
+import org.antlr.v4.runtime.CommonTokenStream;
 import org.antlr.v4.runtime.ParserRuleContext;
 import org.antlr.v4.runtime.RuleContext;
 import org.antlr.v4.runtime.tree.ParseTree;
@@ -29,8 +30,10 @@
 import org.opensearch.sql.ast.expression.subquery.ScalarSubquery;
 import org.opensearch.sql.ast.tree.Trendline;
 import org.opensearch.sql.calcite.plan.OpenSearchConstants;
+import org.opensearch.sql.common.antlr.CaseInsensitiveCharStream;
 import org.opensearch.sql.common.antlr.SyntaxCheckException;
 import org.opensearch.sql.common.utils.StringUtils;
+import org.opensearch.sql.ppl.antlr.parser.OpenSearchPPLLexer;
 import org.opensearch.sql.ppl.antlr.parser.OpenSearchPPLParser;
 import org.opensearch.sql.ppl.antlr.parser.OpenSearchPPLParser.BinaryArithmeticContext;
 import org.opensearch.sql.ppl.antlr.parser.OpenSearchPPLParser.BooleanLiteralContext;
@@ -411,18 +414,51 @@ private Function buildFunction(
         functionName, args.stream().map(this::visitFunctionArg).collect(Collectors.toList()));
   }
 
+  public DataTypeFunctionCallContext createDataTypeFunctionCallContext(String castExpression) {
+    // Create a case-insensitive character stream from the input
+    CaseInsensitiveCharStream charStream = new CaseInsensitiveCharStream(castExpression);
+
+    // Create lexer and parser
+    OpenSearchPPLLexer lexer = new OpenSearchPPLLexer(charStream);
+    CommonTokenStream tokens = new CommonTokenStream(lexer);
+    OpenSearchPPLParser parser = new OpenSearchPPLParser(tokens);
+
+    // Parse the expression - cast is part of evalFunctionCall
+    DataTypeFunctionCallContext evalContext = parser.dataTypeFunctionCall();
+    return evalContext;
+  }
+
   /** Cast function. */
   @Override
   public UnresolvedExpression visitDataTypeFunctionCall(DataTypeFunctionCallContext ctx) {
-    ParseTree rootNode = ctx.getChild(0);
-    String functionName = rootNode.getText();
-    final String mappedName =
-        FUNCTION_NAME_MAPPING.getOrDefault(functionName.toLowerCase(Locale.ROOT), functionName);
-
-    if (mappedName.equals("cast")) {
-      return new Cast(visit(ctx.logicalExpression()), visit(ctx.convertedDataType()));
+    if (ctx.functionArgs() != null) {
+
+      ParseTree rootNode = ctx.getChild(0);
+      String functionName = rootNode.getText();
+      final String mappedName =
+          FUNCTION_NAME_MAPPING.getOrDefault(functionName.toLowerCase(Locale.ROOT), functionName);
+      System.out.println(mappedName);
+      if (mappedName != null && mappedName.equals("tostring")) {
+        if (ctx.functionArgs().functionArg().size() == 1) {
+          List<OpenSearchPPLParser.FunctionArgContext> functionArgs =
+              ctx.functionArgs().functionArg();
+
+          String castExpresstion =
+              String.format("cast( %s as String)", functionArgs.getFirst().getText());
+          DataTypeFunctionCallContext toStringDataTypeConversionContext =
+              this.createDataTypeFunctionCallContext(castExpresstion);
+          return new Cast(
+              visit(toStringDataTypeConversionContext.logicalExpression()),
+              visit(toStringDataTypeConversionContext.convertedDataType()));
+          //
+        } else {
+          return buildFunction(mappedName, ctx.functionArgs().functionArg());
+        }
+      } else {
+        return new Cast(visit(ctx.logicalExpression()), visit(ctx.convertedDataType()));
+      }
     } else {
-      return buildFunction(mappedName, ctx.functionArgs().functionArg());
+      return new Cast(visit(ctx.logicalExpression()), visit(ctx.convertedDataType()));
     }
   }
 
diff --git a/ppl/src/test/java/org/opensearch/sql/ppl/calcite/CalcitePPLStringFunctionTest.java b/ppl/src/test/java/org/opensearch/sql/ppl/calcite/CalcitePPLStringFunctionTest.java
index d41b2c22453..b32ecd04e3f 100644
--- a/ppl/src/test/java/org/opensearch/sql/ppl/calcite/CalcitePPLStringFunctionTest.java
+++ b/ppl/src/test/java/org/opensearch/sql/ppl/calcite/CalcitePPLStringFunctionTest.java
@@ -46,20 +46,55 @@ public void testLower() {
     verifyPPLToSparkSQL(root, expectedSparkSql);
   }
 
+  // This test evalutes tostring where it gets converted to cast call
+
+  @Test
+  public void testToStringFormatNotSpecified() {
+    String ppl =
+        "source=EMP | eval string_value = tostring(MGR) | eval cast_value = cast(MGR as string)|"
+            + " fields string_value, cast_value";
+    RelNode root = getRelNode(ppl);
+    String expectedLogical =
+        "LogicalProject(string_value=[SAFE_CAST($3)], cast_value=[SAFE_CAST($3)])\n"
+            + "  LogicalTableScan(table=[[scott, EMP]])\n";
+    String expectedResult =
+        "string_value=7902; cast_value=7902\n"
+            + "string_value=7698; cast_value=7698\n"
+            + "string_value=7698; cast_value=7698\n"
+            + "string_value=7839; cast_value=7839\n"
+            + "string_value=7698; cast_value=7698\n"
+            + "string_value=7839; cast_value=7839\n"
+            + "string_value=7839; cast_value=7839\n"
+            + "string_value=7566; cast_value=7566\n"
+            + "string_value=null; cast_value=null\n"
+            + "string_value=7698; cast_value=7698\n"
+            + "string_value=7788; cast_value=7788\n"
+            + "string_value=7698; cast_value=7698\n"
+            + "string_value=7566; cast_value=7566\n"
+            + "string_value=7782; cast_value=7782\n";
+    verifyLogical(root, expectedLogical);
+    verifyResult(root, expectedResult);
+
+    String expectedSparkSql =
+        "SELECT SAFE_CAST(`MGR` AS STRING) `string_value`, SAFE_CAST(`MGR` AS STRING)"
+            + " `cast_value`\n"
+            + "FROM `scott`.`EMP`";
+    verifyPPLToSparkSQL(root, expectedSparkSql);
+  }
+
   @Test
   public void testToStringBoolean() {
     String ppl = "source=EMP | eval boolean_value = tostring(1==1) | fields boolean_value |head 1";
     RelNode root = getRelNode(ppl);
     String expectedLogical =
         "LogicalSort(fetch=[1])\n"
-            + "  LogicalProject(boolean_value=[TOSTRING(true)])\n"
+            + "  LogicalProject(boolean_value=['TRUE':VARCHAR])\n"
             + "    LogicalTableScan(table=[[scott, EMP]])\n";
-    String expectedResult = "boolean_value=True\n";
+    String expectedResult = "boolean_value=TRUE\n";
     verifyLogical(root, expectedLogical);
     verifyResult(root, expectedResult);
 
-    String expectedSparkSql =
-        "SELECT `TOSTRING`(TRUE) `boolean_value`\n" + "FROM `scott`.`EMP`\n" + "LIMIT 1";
+    String expectedSparkSql = "SELECT 'TRUE' `boolean_value`\nFROM `scott`.`EMP`\nLIMIT 1";
     verifyPPLToSparkSQL(root, expectedSparkSql);
   }
 
@@ -126,56 +161,70 @@ public void testToStringHex() {
     verifyPPLToSparkSQL(root, expectedSparkSql);
   }
 
-    @Test
-    public void testToStringHexFromNumberAsString() {
-        String ppl =
-                "source=EMP |  eval salary_hex = tostring(\"1600\", \"hex\") | fields ENAME, salary_hex| head 1";
-        RelNode root = getRelNode(ppl);
-        String expectedLogical =
-                "LogicalSort(fetch=[1])\n  LogicalProject(ENAME=[$1], salary_hex=[TOSTRING('1600':VARCHAR, 'hex':VARCHAR)])\n    LogicalTableScan(table=[[scott, EMP]])\n";
-        String expectedResult =
-                "ENAME=SMITH; salary_hex=640\n";
-        verifyLogical(root, expectedLogical);
-        verifyResult(root, expectedResult);
-
-        String expectedSparkSql =
-                "SELECT `ENAME`, `TOSTRING`('1600', 'hex') `salary_hex`\nFROM `scott`.`EMP`\nLIMIT 1";
-        verifyPPLToSparkSQL(root, expectedSparkSql);
-    }
-
-    @Test
-    public void testToStringCommaFromNumberAsString() {
-        String ppl =
-                "source=EMP |  eval salary_comma = tostring(\"160040222\", \"commas\") | fields ENAME, salary_comma| head 1";
-        RelNode root = getRelNode(ppl);
-        String expectedLogical =
-                "LogicalSort(fetch=[1])\n  LogicalProject(ENAME=[$1], salary_comma=[TOSTRING('160040222':VARCHAR, 'commas':VARCHAR)])\n    LogicalTableScan(table=[[scott, EMP]])\n";
-        String expectedResult =
-                "ENAME=SMITH; salary_comma=160,040,222\n";
-        verifyLogical(root, expectedLogical);
-        verifyResult(root, expectedResult);
-
-        String expectedSparkSql =
-                "SELECT `ENAME`, `TOSTRING`('160040222', 'commas') `salary_comma`\nFROM `scott`.`EMP`\nLIMIT 1";
-        verifyPPLToSparkSQL(root, expectedSparkSql);
-    }
-    @Test
-    public void testToStringBinaryFromNumberAsString() {
-        String ppl =
-                "source=EMP |  eval salary_binary = tostring(\"160040222\", \"binary\") | fields ENAME, salary_binary| head 1";
-        RelNode root = getRelNode(ppl);
-        String expectedLogical =
-                "LogicalSort(fetch=[1])\n  LogicalProject(ENAME=[$1], salary_binary=[TOSTRING('160040222':VARCHAR, 'binary':VARCHAR)])\n    LogicalTableScan(table=[[scott, EMP]])\n";
-        String expectedResult =
-                "ENAME=SMITH; salary_binary=1001100010100000010100011110\n";
-        verifyLogical(root, expectedLogical);
-        verifyResult(root, expectedResult);
-
-        String expectedSparkSql =
-                "SELECT `ENAME`, `TOSTRING`('160040222', 'binary') `salary_binary`\nFROM `scott`.`EMP`\nLIMIT 1";
-        verifyPPLToSparkSQL(root, expectedSparkSql);
-    }
-    @Test
+  @Test
+  public void testToStringHexFromNumberAsString() {
+    String ppl =
+        "source=EMP |  eval salary_hex = tostring(\"1600\", \"hex\") | fields ENAME, salary_hex|"
+            + " head 1";
+    RelNode root = getRelNode(ppl);
+    String expectedLogical =
+        "LogicalSort(fetch=[1])\n"
+            + "  LogicalProject(ENAME=[$1], salary_hex=[TOSTRING('1600':VARCHAR, 'hex':VARCHAR)])\n"
+            + "    LogicalTableScan(table=[[scott, EMP]])\n";
+    String expectedResult = "ENAME=SMITH; salary_hex=640\n";
+    verifyLogical(root, expectedLogical);
+    verifyResult(root, expectedResult);
+
+    String expectedSparkSql =
+        "SELECT `ENAME`, `TOSTRING`('1600', 'hex') `salary_hex`\nFROM `scott`.`EMP`\nLIMIT 1";
+    verifyPPLToSparkSQL(root, expectedSparkSql);
+  }
+
+  @Test
+  public void testToStringCommaFromNumberAsString() {
+    String ppl =
+        "source=EMP |  eval salary_comma = tostring(\"160040222\", \"commas\") | fields ENAME,"
+            + " salary_comma| head 1";
+    RelNode root = getRelNode(ppl);
+    String expectedLogical =
+        "LogicalSort(fetch=[1])\n"
+            + "  LogicalProject(ENAME=[$1], salary_comma=[TOSTRING('160040222':VARCHAR,"
+            + " 'commas':VARCHAR)])\n"
+            + "    LogicalTableScan(table=[[scott, EMP]])\n";
+    String expectedResult = "ENAME=SMITH; salary_comma=160,040,222\n";
+    verifyLogical(root, expectedLogical);
+    verifyResult(root, expectedResult);
+
+    String expectedSparkSql =
+        "SELECT `ENAME`, `TOSTRING`('160040222', 'commas') `salary_comma`\n"
+            + "FROM `scott`.`EMP`\n"
+            + "LIMIT 1";
+    verifyPPLToSparkSQL(root, expectedSparkSql);
+  }
+
+  @Test
+  public void testToStringBinaryFromNumberAsString() {
+    String ppl =
+        "source=EMP |  eval salary_binary = tostring(\"160040222\", \"binary\") | fields ENAME,"
+            + " salary_binary| head 1";
+    RelNode root = getRelNode(ppl);
+    String expectedLogical =
+        "LogicalSort(fetch=[1])\n"
+            + "  LogicalProject(ENAME=[$1], salary_binary=[TOSTRING('160040222':VARCHAR,"
+            + " 'binary':VARCHAR)])\n"
+            + "    LogicalTableScan(table=[[scott, EMP]])\n";
+    String expectedResult = "ENAME=SMITH; salary_binary=1001100010100000010100011110\n";
+    verifyLogical(root, expectedLogical);
+    verifyResult(root, expectedResult);
+
+    String expectedSparkSql =
+        "SELECT `ENAME`, `TOSTRING`('160040222', 'binary') `salary_binary`\n"
+            + "FROM `scott`.`EMP`\n"
+            + "LIMIT 1";
+    verifyPPLToSparkSQL(root, expectedSparkSql);
+  }
+
+  @Test
   public void testToStringCommas() {
     String ppl =
         "source=EMP |  eval salary_commas = tostring(SAL, \"commas\") | fields ENAME,"

From 6e24aa3c4b16f6a5734db18f210b8b5c1f5f245f Mon Sep 17 00:00:00 2001
From: Asif Bashar <asif.bashar@gmail.com>
Date: Fri, 17 Oct 2025 13:32:18 -0700
Subject: [PATCH 11/24] added doc update to specifically set 2nd argument as
 optional

Signed-off-by: Asif Bashar <asif.bashar@gmail.com>
---
 docs/user/ppl/functions/conversion.rst | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/docs/user/ppl/functions/conversion.rst b/docs/user/ppl/functions/conversion.rst
index 036a89daf00..9f9646efef4 100644
--- a/docs/user/ppl/functions/conversion.rst
+++ b/docs/user/ppl/functions/conversion.rst
@@ -86,10 +86,10 @@ Description
 >>>>>>>>>>>
 The following usage options are available, depending on the parameter types and the number of parameters.
 
-Usage with format type: tostring(ANY, [format]): Converts the number in first argument  to provided format type string in second argument. If non number type, then it converts to default string representation.
+Usage with format type: tostring(ANY, [format]): Converts the number in first argument  to provided format type string in second argument. If second argument is not provided, then it converts to default string representation.
 Return type: string
 
-Usage for boolean parameter without format type tostring(boolean): Converts the string to 'True' or 'False'.
+Usage for boolean parameter without format type tostring(boolean): Converts the string to 'TRUE' or 'FALSE'.
 Return type: string
 
 You can use this function with the eval commands and as part of eval expressions. If first argument can be any valid type , second argument is optional and if provided , it needs to be format name to convert to where first argument contains only numbers. If first argument is boolean, then second argument is not used even if its provided.
@@ -100,12 +100,13 @@ a) "binary" Converts a number to a binary value.
 b) "hex" Converts the number to a hexadecimal value.
 c) "commas" Formats the number with commas. If the number includes a decimal, the function rounds the number to nearest two decimal places.
 d) "duration" Converts the value in seconds to the readable time format HH:MM:SS.
+5) "duration_millis" Converts the value in milliseconds to the readable time format HH:MM:SS.
 
 The format argument is optional and is only used when the value argument is a number. The tostring function supports the following formats.
 
 Basic examples:
 
-The following example returns "True 0xF 12,345.68".
+The following example returns "TRUE 0xF 12,345.68".
 
     ... | eval n=tostring(1==1) + " " + tostring(15, "hex") + " " + tostring(12345.6789, "commas")
 
@@ -169,5 +170,5 @@ Example::
     +---------------------+
     | boolean_str         |
     |---------------------+
-    | True                |
+    | TRUE                |
     +---------------------+
\ No newline at end of file

From 454cfc8db324866376f2452290b0fd0739008754 Mon Sep 17 00:00:00 2001
From: Asif Bashar <asif.bashar@gmail.com>
Date: Fri, 17 Oct 2025 13:33:59 -0700
Subject: [PATCH 12/24] mentioned as value instead of number specifically

Signed-off-by: Asif Bashar <asif.bashar@gmail.com>
---
 docs/user/ppl/functions/conversion.rst | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/docs/user/ppl/functions/conversion.rst b/docs/user/ppl/functions/conversion.rst
index 9f9646efef4..4f2d432c71a 100644
--- a/docs/user/ppl/functions/conversion.rst
+++ b/docs/user/ppl/functions/conversion.rst
@@ -86,7 +86,7 @@ Description
 >>>>>>>>>>>
 The following usage options are available, depending on the parameter types and the number of parameters.
 
-Usage with format type: tostring(ANY, [format]): Converts the number in first argument  to provided format type string in second argument. If second argument is not provided, then it converts to default string representation.
+Usage with format type: tostring(ANY, [format]): Converts the value in first argument  to provided format type string in second argument. If second argument is not provided, then it converts to default string representation.
 Return type: string
 
 Usage for boolean parameter without format type tostring(boolean): Converts the string to 'TRUE' or 'FALSE'.

From b221e8c4f583b947198253ee90b5edb6f15b382a Mon Sep 17 00:00:00 2001
From: Asif Bashar <asif.bashar@gmail.com>
Date: Fri, 17 Oct 2025 13:46:56 -0700
Subject: [PATCH 13/24] fixed wrong bullet point

Signed-off-by: Asif Bashar <asif.bashar@gmail.com>
---
 docs/user/ppl/functions/conversion.rst | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/docs/user/ppl/functions/conversion.rst b/docs/user/ppl/functions/conversion.rst
index 4f2d432c71a..708bde1fa11 100644
--- a/docs/user/ppl/functions/conversion.rst
+++ b/docs/user/ppl/functions/conversion.rst
@@ -100,7 +100,7 @@ a) "binary" Converts a number to a binary value.
 b) "hex" Converts the number to a hexadecimal value.
 c) "commas" Formats the number with commas. If the number includes a decimal, the function rounds the number to nearest two decimal places.
 d) "duration" Converts the value in seconds to the readable time format HH:MM:SS.
-5) "duration_millis" Converts the value in milliseconds to the readable time format HH:MM:SS.
+e) "duration_millis" Converts the value in milliseconds to the readable time format HH:MM:SS.
 
 The format argument is optional and is only used when the value argument is a number. The tostring function supports the following formats.
 

From 1ed88e1dc190096617571796a14d9b8d76ba338e Mon Sep 17 00:00:00 2001
From: Asif Bashar <asif.bashar@gmail.com>
Date: Mon, 20 Oct 2025 09:38:56 -0700
Subject: [PATCH 14/24] removed extra quote

Signed-off-by: Asif Bashar <asif.bashar@gmail.com>
---
 docs/user/ppl/functions/conversion.rst | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/docs/user/ppl/functions/conversion.rst b/docs/user/ppl/functions/conversion.rst
index 708bde1fa11..6e2149494c3 100644
--- a/docs/user/ppl/functions/conversion.rst
+++ b/docs/user/ppl/functions/conversion.rst
@@ -119,7 +119,7 @@ The following example returns foo=615 and foo2=00:10:15. The 615 seconds is conv
 You can use this function to convert a number to a string of its binary representation.
 Example::
 
-    os> source=EMP |  eval salary_binary = tostring(SAL, "binary") | fields ENAME, salary_binary, SAL"
+    os> source=EMP |  eval salary_binary = tostring(SAL, "binary") | fields ENAME, salary_binary, SAL
     fetched rows / total rows = 1/1
     +---------------+------------------+------------+
     | ENAME         |   salary_binary  |  SAL       |
@@ -131,7 +131,7 @@ Example::
 You can use this function to convert a number to a string of its hex representation.
 Example::
 
-    os> source=EMP |  eval salary_hex = tostring(SAL, "hex") | fields ENAME, salary_hex, SAL"
+    os> source=EMP |  eval salary_hex = tostring(SAL, "hex") | fields ENAME, salary_hex, SAL
     fetched rows / total rows = 1/1
     +---------------+------------------+------------+
     | ENAME         |   salary_hex  |  SAL          |
@@ -142,7 +142,7 @@ Example::
 The following example formats the column totalSales to display values  with commas.
 Example::
 
-     os> source=EMP |  eval salary_commas = tostring(SAL, "commas") | fields ENAME, salary_commas, SAL"
+     os> source=EMP |  eval salary_commas = tostring(SAL, "commas") | fields ENAME, salary_commas, SAL
      fetched rows / total rows = 1/1
     +---------------+------------------+------------+
     | ENAME         |   salary_commas  |  SAL       |
@@ -153,7 +153,7 @@ Example::
 The following example converts number of seconds to HH:MM:SS format representing hours, minutes and seconds.
 Example::
 
-      os> source=EMP |  eval duration = tostring(6500, "duration") | fields ENAME, duration"
+      os> source=EMP |  eval duration = tostring(6500, "duration") | fields ENAME, duration
           fetched rows / total rows = 1/1
     +---------------+-------------+
     | ENAME         |   duration  |

From 5cbedccd57c6862925fce874720def1afea82892 Mon Sep 17 00:00:00 2001
From: Asif Bashar <asif.bashar@gmail.com>
Date: Mon, 20 Oct 2025 17:28:04 -0700
Subject: [PATCH 15/24] we have duplicated example

Signed-off-by: Asif Bashar <asif.bashar@gmail.com>
---
 docs/user/ppl/functions/conversion.rst | 10 ----------
 1 file changed, 10 deletions(-)

diff --git a/docs/user/ppl/functions/conversion.rst b/docs/user/ppl/functions/conversion.rst
index 6e2149494c3..61be5b64362 100644
--- a/docs/user/ppl/functions/conversion.rst
+++ b/docs/user/ppl/functions/conversion.rst
@@ -106,16 +106,6 @@ The format argument is optional and is only used when the value argument is a nu
 
 Basic examples:
 
-The following example returns "TRUE 0xF 12,345.68".
-
-    ... | eval n=tostring(1==1) + " " + tostring(15, "hex") + " " + tostring(12345.6789, "commas")
-
-The following example returns foo=615 and foo2=00:10:15. The 615 seconds is converted into minutes and seconds.
-
-    ... | eval foo=615 | eval foo2 = tostring(foo, "duration")
-
-
-
 You can use this function to convert a number to a string of its binary representation.
 Example::
 

From 682eb9d8d57a72ee30570744e7ba428a6dfcfbe7 Mon Sep 17 00:00:00 2001
From: Asif Bashar <asif.bashar@gmail.com>
Date: Mon, 20 Oct 2025 21:28:05 -0700
Subject: [PATCH 16/24] applied recommended changes

Signed-off-by: Asif Bashar <asif.bashar@gmail.com>
---
 .../sql/calcite/CalciteRexNodeVisitor.java    | 10 +++-
 .../function/udf/ToStringFunction.java        | 10 ++--
 ppl/src/main/antlr/OpenSearchPPLParser.g4     |  4 +-
 .../sql/ppl/parser/AstExpressionBuilder.java  | 47 +------------------
 .../calcite/CalcitePPLStringFunctionTest.java |  5 +-
 5 files changed, 17 insertions(+), 59 deletions(-)

diff --git a/core/src/main/java/org/opensearch/sql/calcite/CalciteRexNodeVisitor.java b/core/src/main/java/org/opensearch/sql/calcite/CalciteRexNodeVisitor.java
index bb6f16b2e8a..b1be49582ec 100644
--- a/core/src/main/java/org/opensearch/sql/calcite/CalciteRexNodeVisitor.java
+++ b/core/src/main/java/org/opensearch/sql/calcite/CalciteRexNodeVisitor.java
@@ -417,11 +417,19 @@ public RexNode visitFunction(Function node, CalcitePlanContext context) {
         context.setInCoalesceFunction(false);
       }
     }
-
+    if (node.getFuncName().equalsIgnoreCase("tostring") && args.size() == 1) {
+      RelDataType targetType =
+          context.relBuilder.getTypeFactory().createSqlType(SqlTypeName.VARCHAR);
+      // Get the source expression from arguments
+      RexNode sourceExpression = arguments.get(0);
+      // Create cast RexNode using ExtendedRexBuilder
+      return context.rexBuilder.makeCast(targetType, sourceExpression);
+    }
     RexNode resolvedNode =
         PPLFuncImpTable.INSTANCE.resolve(
             context.rexBuilder, node.getFuncName(), arguments.toArray(new RexNode[0]));
     if (resolvedNode != null) {
+
       return resolvedNode;
     }
     throw new IllegalArgumentException("Unsupported operator: " + node.getFuncName());
diff --git a/core/src/main/java/org/opensearch/sql/expression/function/udf/ToStringFunction.java b/core/src/main/java/org/opensearch/sql/expression/function/udf/ToStringFunction.java
index be76100f38d..1052a8f5f11 100644
--- a/core/src/main/java/org/opensearch/sql/expression/function/udf/ToStringFunction.java
+++ b/core/src/main/java/org/opensearch/sql/expression/function/udf/ToStringFunction.java
@@ -18,6 +18,7 @@
 import org.apache.calcite.linq4j.tree.Expressions;
 import org.apache.calcite.rex.RexCall;
 import org.apache.calcite.runtime.SqlFunctions;
+import org.apache.calcite.sql.*;
 import org.apache.calcite.sql.type.SqlReturnTypeInference;
 import org.opensearch.sql.calcite.utils.PPLOperandTypes;
 import org.opensearch.sql.calcite.utils.PPLReturnTypes;
@@ -65,17 +66,12 @@ public static class ToStringImplementor implements NotNullImplementor {
     public Expression implement(
         RexToLixTranslator translator, RexCall call, List<Expression> translatedOperands) {
       Expression fieldValue = translatedOperands.get(0);
+
       if (translatedOperands.size() > 1) {
         Expression format = translatedOperands.get(1);
         return Expressions.call(ToStringFunction.class, "toString", fieldValue, format);
       } else {
-        // autoboxes to Boolean
-
-        if (!fieldValue.getType().getTypeName().equals("Boolean")) {
-          return Expressions.call(ToStringFunction.class, "toString", fieldValue);
-        } else {
-          return Expressions.call(ToStringFunction.class, "toString", fieldValue);
-        }
+        return Expressions.call(ToStringFunction.class, "toString", fieldValue);
       }
     }
   }
diff --git a/ppl/src/main/antlr/OpenSearchPPLParser.g4 b/ppl/src/main/antlr/OpenSearchPPLParser.g4
index 852c55c863c..4c4fa3bbac6 100644
--- a/ppl/src/main/antlr/OpenSearchPPLParser.g4
+++ b/ppl/src/main/antlr/OpenSearchPPLParser.g4
@@ -848,10 +848,9 @@ evalFunctionCall
    ;
 
 
-// cast, tostring function
+// cast function
 dataTypeFunctionCall
    : CAST LT_PRTHS logicalExpression AS convertedDataType RT_PRTHS
-   | TOSTRING LT_PRTHS functionArgs RT_PRTHS
    ;
 
 
@@ -1219,6 +1218,7 @@ systemFunctionName
 textFunctionName
    : SUBSTR
    | SUBSTRING
+   | TOSTRING
    | TRIM
    | LTRIM
    | RTRIM
diff --git a/ppl/src/main/java/org/opensearch/sql/ppl/parser/AstExpressionBuilder.java b/ppl/src/main/java/org/opensearch/sql/ppl/parser/AstExpressionBuilder.java
index 2112282f728..f037376f5c2 100644
--- a/ppl/src/main/java/org/opensearch/sql/ppl/parser/AstExpressionBuilder.java
+++ b/ppl/src/main/java/org/opensearch/sql/ppl/parser/AstExpressionBuilder.java
@@ -19,7 +19,6 @@
 import java.util.stream.Collectors;
 import java.util.stream.IntStream;
 import java.util.stream.Stream;
-import org.antlr.v4.runtime.CommonTokenStream;
 import org.antlr.v4.runtime.ParserRuleContext;
 import org.antlr.v4.runtime.RuleContext;
 import org.antlr.v4.runtime.tree.ParseTree;
@@ -30,10 +29,8 @@
 import org.opensearch.sql.ast.expression.subquery.ScalarSubquery;
 import org.opensearch.sql.ast.tree.Trendline;
 import org.opensearch.sql.calcite.plan.OpenSearchConstants;
-import org.opensearch.sql.common.antlr.CaseInsensitiveCharStream;
 import org.opensearch.sql.common.antlr.SyntaxCheckException;
 import org.opensearch.sql.common.utils.StringUtils;
-import org.opensearch.sql.ppl.antlr.parser.OpenSearchPPLLexer;
 import org.opensearch.sql.ppl.antlr.parser.OpenSearchPPLParser;
 import org.opensearch.sql.ppl.antlr.parser.OpenSearchPPLParser.BinaryArithmeticContext;
 import org.opensearch.sql.ppl.antlr.parser.OpenSearchPPLParser.BooleanLiteralContext;
@@ -414,52 +411,10 @@ private Function buildFunction(
         functionName, args.stream().map(this::visitFunctionArg).collect(Collectors.toList()));
   }
 
-  public DataTypeFunctionCallContext createDataTypeFunctionCallContext(String castExpression) {
-    // Create a case-insensitive character stream from the input
-    CaseInsensitiveCharStream charStream = new CaseInsensitiveCharStream(castExpression);
-
-    // Create lexer and parser
-    OpenSearchPPLLexer lexer = new OpenSearchPPLLexer(charStream);
-    CommonTokenStream tokens = new CommonTokenStream(lexer);
-    OpenSearchPPLParser parser = new OpenSearchPPLParser(tokens);
-
-    // Parse the expression - cast is part of evalFunctionCall
-    DataTypeFunctionCallContext evalContext = parser.dataTypeFunctionCall();
-    return evalContext;
-  }
-
   /** Cast function. */
   @Override
   public UnresolvedExpression visitDataTypeFunctionCall(DataTypeFunctionCallContext ctx) {
-    if (ctx.functionArgs() != null) {
-
-      ParseTree rootNode = ctx.getChild(0);
-      String functionName = rootNode.getText();
-      final String mappedName =
-          FUNCTION_NAME_MAPPING.getOrDefault(functionName.toLowerCase(Locale.ROOT), functionName);
-      System.out.println(mappedName);
-      if (mappedName != null && mappedName.equals("tostring")) {
-        if (ctx.functionArgs().functionArg().size() == 1) {
-          List<OpenSearchPPLParser.FunctionArgContext> functionArgs =
-              ctx.functionArgs().functionArg();
-
-          String castExpresstion =
-              String.format("cast( %s as String)", functionArgs.getFirst().getText());
-          DataTypeFunctionCallContext toStringDataTypeConversionContext =
-              this.createDataTypeFunctionCallContext(castExpresstion);
-          return new Cast(
-              visit(toStringDataTypeConversionContext.logicalExpression()),
-              visit(toStringDataTypeConversionContext.convertedDataType()));
-          //
-        } else {
-          return buildFunction(mappedName, ctx.functionArgs().functionArg());
-        }
-      } else {
-        return new Cast(visit(ctx.logicalExpression()), visit(ctx.convertedDataType()));
-      }
-    } else {
-      return new Cast(visit(ctx.logicalExpression()), visit(ctx.convertedDataType()));
-    }
+    return new Cast(visit(ctx.logicalExpression()), visit(ctx.convertedDataType()));
   }
 
   @Override
diff --git a/ppl/src/test/java/org/opensearch/sql/ppl/calcite/CalcitePPLStringFunctionTest.java b/ppl/src/test/java/org/opensearch/sql/ppl/calcite/CalcitePPLStringFunctionTest.java
index b32ecd04e3f..c06c536919c 100644
--- a/ppl/src/test/java/org/opensearch/sql/ppl/calcite/CalcitePPLStringFunctionTest.java
+++ b/ppl/src/test/java/org/opensearch/sql/ppl/calcite/CalcitePPLStringFunctionTest.java
@@ -55,7 +55,7 @@ public void testToStringFormatNotSpecified() {
             + " fields string_value, cast_value";
     RelNode root = getRelNode(ppl);
     String expectedLogical =
-        "LogicalProject(string_value=[SAFE_CAST($3)], cast_value=[SAFE_CAST($3)])\n"
+        "LogicalProject(string_value=[CAST($3):VARCHAR NOT NULL], cast_value=[SAFE_CAST($3)])\n"
             + "  LogicalTableScan(table=[[scott, EMP]])\n";
     String expectedResult =
         "string_value=7902; cast_value=7902\n"
@@ -76,8 +76,7 @@ public void testToStringFormatNotSpecified() {
     verifyResult(root, expectedResult);
 
     String expectedSparkSql =
-        "SELECT SAFE_CAST(`MGR` AS STRING) `string_value`, SAFE_CAST(`MGR` AS STRING)"
-            + " `cast_value`\n"
+        "SELECT CAST(`MGR` AS STRING) `string_value`, SAFE_CAST(`MGR` AS STRING) `cast_value`\n"
             + "FROM `scott`.`EMP`";
     verifyPPLToSparkSQL(root, expectedSparkSql);
   }

From d0b809a2db65599be273a1600a14f224d415f679 Mon Sep 17 00:00:00 2001
From: Asif Bashar <abashar@apple.com>
Date: Sat, 25 Oct 2025 20:14:25 -0700
Subject: [PATCH 17/24] recommended changes

Signed-off-by: Asif Bashar <asif.bashar@gmail.com>
---
 .../sql/calcite/utils/PPLOperandTypes.java    |  5 +-
 .../expression/function/PPLFuncImpTable.java  |  6 ++
 .../function/udf/ToStringFunction.java        | 75 +++----------------
 .../function/udf/ToStringFunctionTest.java    | 15 +---
 docs/user/ppl/functions/conversion.rst        | 14 ++--
 5 files changed, 26 insertions(+), 89 deletions(-)

diff --git a/core/src/main/java/org/opensearch/sql/calcite/utils/PPLOperandTypes.java b/core/src/main/java/org/opensearch/sql/calcite/utils/PPLOperandTypes.java
index 20811f1af48..e2bdc2f02e3 100644
--- a/core/src/main/java/org/opensearch/sql/calcite/utils/PPLOperandTypes.java
+++ b/core/src/main/java/org/opensearch/sql/calcite/utils/PPLOperandTypes.java
@@ -112,11 +112,10 @@ private PPLOperandTypes() {}
               SqlTypeFamily.INTEGER,
               SqlTypeFamily.INTEGER));
 
-  public static final UDFOperandMetadata BOOLEAN_OR_NUMERIC_STRING_OR_STRING_STRING =
+  public static final UDFOperandMetadata NUMERIC_STRING_OR_STRING_STRING =
       UDFOperandMetadata.wrap(
           (CompositeOperandTypeChecker)
-              OperandTypes.family(SqlTypeFamily.BOOLEAN)
-                  .or(OperandTypes.family(SqlTypeFamily.NUMERIC, SqlTypeFamily.STRING))
+              (OperandTypes.family(SqlTypeFamily.NUMERIC, SqlTypeFamily.STRING))
                   .or(OperandTypes.family(SqlTypeFamily.STRING, SqlTypeFamily.STRING)));
 
   public static final UDFOperandMetadata NUMERIC_NUMERIC_OPTIONAL_NUMERIC =
diff --git a/core/src/main/java/org/opensearch/sql/expression/function/PPLFuncImpTable.java b/core/src/main/java/org/opensearch/sql/expression/function/PPLFuncImpTable.java
index de89df383d2..9a26569e493 100644
--- a/core/src/main/java/org/opensearch/sql/expression/function/PPLFuncImpTable.java
+++ b/core/src/main/java/org/opensearch/sql/expression/function/PPLFuncImpTable.java
@@ -889,6 +889,12 @@ void populate() {
 
       registerOperator(INTERNAL_PATTERN_PARSER, PPLBuiltinOperators.PATTERN_PARSER);
       registerOperator(TOSTRING, PPLBuiltinOperators.TOSTRING);
+      register(
+          TOSTRING,
+          (FunctionImp1)
+              (builder, source) ->
+                  builder.makeCast(TYPE_FACTORY.createSqlType(SqlTypeName.VARCHAR, true), source),
+          PPLTypeChecker.family(SqlTypeFamily.ANY));
 
       // Register MVJOIN to use Calcite's ARRAY_JOIN
       register(
diff --git a/core/src/main/java/org/opensearch/sql/expression/function/udf/ToStringFunction.java b/core/src/main/java/org/opensearch/sql/expression/function/udf/ToStringFunction.java
index 1052a8f5f11..46d0ada1419 100644
--- a/core/src/main/java/org/opensearch/sql/expression/function/udf/ToStringFunction.java
+++ b/core/src/main/java/org/opensearch/sql/expression/function/udf/ToStringFunction.java
@@ -48,7 +48,7 @@ public ToStringFunction() {
   public static final String BINARY_FORMAT = "binary";
   public static final SqlFunctions.DateFormatFunction dateTimeFormatter =
       new SqlFunctions.DateFormatFunction();
-  public static final String format24hour = "%H:%M:%S"; // 24-hour format
+  public static final String FORMAT_24_HOUR = "%H:%M:%S";
 
   @Override
   public SqlReturnTypeInference getReturnTypeInference() {
@@ -57,7 +57,7 @@ public SqlReturnTypeInference getReturnTypeInference() {
 
   @Override
   public UDFOperandMetadata getOperandMetadata() {
-    return PPLOperandTypes.BOOLEAN_OR_NUMERIC_STRING_OR_STRING_STRING;
+    return PPLOperandTypes.NUMERIC_STRING_OR_STRING_STRING;
   }
 
   public static class ToStringImplementor implements NotNullImplementor {
@@ -66,39 +66,20 @@ public static class ToStringImplementor implements NotNullImplementor {
     public Expression implement(
         RexToLixTranslator translator, RexCall call, List<Expression> translatedOperands) {
       Expression fieldValue = translatedOperands.get(0);
-
-      if (translatedOperands.size() > 1) {
-        Expression format = translatedOperands.get(1);
-        return Expressions.call(ToStringFunction.class, "toString", fieldValue, format);
-      } else {
-        return Expressions.call(ToStringFunction.class, "toString", fieldValue);
-      }
-    }
-  }
-
-  @Strict
-  public static String toString(boolean fieldValue) {
-    if (fieldValue) {
-      return "True";
-    } else {
-      return "False";
+      Expression format = translatedOperands.get(1);
+      return Expressions.call(ToStringFunction.class, "toString", fieldValue, format);
     }
   }
 
-  @Strict
-  public static String toString(String fieldValue) {
-    return toString(Boolean.parseBoolean(fieldValue));
-  }
-
   @Strict
   public static String toString(BigDecimal num, String format) {
     if (format.equals(DURATION_FORMAT)) {
 
-      return dateTimeFormatter.formatTime(format24hour, num.toBigInteger().intValue() * 1000);
+      return dateTimeFormatter.formatTime(FORMAT_24_HOUR, num.toBigInteger().intValue() * 1000);
 
     } else if (format.equals(DURATION_MILLIS_FORMAT)) {
 
-      return dateTimeFormatter.formatTime(format24hour, num.toBigInteger().intValue());
+      return dateTimeFormatter.formatTime(FORMAT_24_HOUR, num.toBigInteger().intValue());
 
     } else if (format.equals(HEX_FORMAT)) {
       return num.toBigInteger().toString(16);
@@ -117,53 +98,17 @@ public static String toString(BigDecimal num, String format) {
 
   @Strict
   public static String toString(double num, String format) {
-    if (format.equals(DURATION_FORMAT)) {
-      return dateTimeFormatter.formatTime(format24hour, ((int) Math.round(num)) * 1000);
-    } else if (format.equals(DURATION_MILLIS_FORMAT)) {
-
-      return dateTimeFormatter.formatTime(format24hour, ((int) Math.round(num)));
-
-    } else if (format.equals(HEX_FORMAT)) {
-      return Double.toHexString(num);
-    } else if (format.equals(COMMAS_FORMAT)) {
-      NumberFormat nf = NumberFormat.getNumberInstance(Locale.getDefault());
-      return nf.format(num);
-    } else if (format.equals(BINARY_FORMAT)) {
-      return Long.toBinaryString(Double.doubleToLongBits(num));
-    }
-    return Double.toString(num);
-  }
-
-  @Strict
-  public static String toString(short num, String format) {
-    int i = (int) num;
-    return toString(i, format);
+    return toString(BigDecimal.valueOf(num), format);
   }
 
   @Strict
   public static String toString(int num, String format) {
-
-    if (format.equals(DURATION_FORMAT)) {
-      return dateTimeFormatter.formatTime(format24hour, num * 1000);
-    } else if (format.equals(DURATION_MILLIS_FORMAT)) {
-      return dateTimeFormatter.formatTime(format24hour, num);
-    } else if (format.equals(HEX_FORMAT)) {
-      return Integer.toHexString(num);
-    } else if (format.equals(COMMAS_FORMAT)) {
-      NumberFormat nf = NumberFormat.getNumberInstance(Locale.getDefault());
-      return nf.format(num);
-    } else if (format.equals(BINARY_FORMAT)) {
-      return Integer.toBinaryString(num);
-    }
-    return Integer.toString(num);
+    return toString(BigDecimal.valueOf(num), format);
   }
 
   @Strict
   public static String toString(String str, String format) {
-    if (str.contains(".") || (str.length() > 10)) {
-      return toString(Double.parseDouble(str), format);
-    } else {
-      return toString(Integer.parseInt(str), format);
-    }
+    BigDecimal bd = new BigDecimal(str);
+    return toString(bd, format);
   }
 }
diff --git a/core/src/test/java/org/opensearch/sql/expression/function/udf/ToStringFunctionTest.java b/core/src/test/java/org/opensearch/sql/expression/function/udf/ToStringFunctionTest.java
index f0867f93327..e29d6c10d19 100644
--- a/core/src/test/java/org/opensearch/sql/expression/function/udf/ToStringFunctionTest.java
+++ b/core/src/test/java/org/opensearch/sql/expression/function/udf/ToStringFunctionTest.java
@@ -15,19 +15,6 @@ public class ToStringFunctionTest {
 
   private final ToStringFunction function = new ToStringFunction();
 
-  @Test
-  void testBooleanToString() {
-    assertEquals("True", ToStringFunction.toString(true));
-    assertEquals("False", ToStringFunction.toString(false));
-  }
-
-  @Test
-  void testStringBooleanToString() {
-    assertEquals("True", ToStringFunction.toString("true"));
-    assertEquals("False", ToStringFunction.toString("false"));
-    assertEquals("False", ToStringFunction.toString("anythingElse"));
-  }
-
   @Test
   void testBigDecimalToStringDurationFormat() {
     BigDecimal num = new BigDecimal("3661"); // 1 hour 1 minute 1 second
@@ -74,7 +61,7 @@ void testDoubleToStringDurationFormat() {
   void testDoubleToStringHexFormat() {
     double num = 10.5;
     String result = ToStringFunction.toString(num, ToStringFunction.HEX_FORMAT);
-    assertTrue(result.startsWith("0x"));
+    assertTrue(result.equals("a"));
   }
 
   @Test
diff --git a/docs/user/ppl/functions/conversion.rst b/docs/user/ppl/functions/conversion.rst
index 61be5b64362..c9ee1576037 100644
--- a/docs/user/ppl/functions/conversion.rst
+++ b/docs/user/ppl/functions/conversion.rst
@@ -123,16 +123,16 @@ Example::
 
     os> source=EMP |  eval salary_hex = tostring(SAL, "hex") | fields ENAME, salary_hex, SAL
     fetched rows / total rows = 1/1
-    +---------------+------------------+------------+
-    | ENAME         |   salary_hex  |  SAL          |
-    |---------------+------------------+------------+
-    | SMITH         |   13880       | 80000.00      |
-    +---------------+---------------+---------------+
+    +---------------+---------------+------------+
+    | ENAME         |   salary_hex  |  SAL       |
+    |---------------+------------------+---------+
+    | SMITH         |   13880       | 80000.00   |
+    +---------------+---------------+------------+
 
 The following example formats the column totalSales to display values  with commas.
 Example::
 
-     os> source=EMP |  eval salary_commas = tostring(SAL, "commas") | fields ENAME, salary_commas, SAL
+    os> source=EMP |  eval salary_commas = tostring(SAL, "commas") | fields ENAME, salary_commas, SAL
      fetched rows / total rows = 1/1
     +---------------+------------------+------------+
     | ENAME         |   salary_commas  |  SAL       |
@@ -143,7 +143,7 @@ Example::
 The following example converts number of seconds to HH:MM:SS format representing hours, minutes and seconds.
 Example::
 
-      os> source=EMP |  eval duration = tostring(6500, "duration") | fields ENAME, duration
+    os> source=EMP |  eval duration = tostring(6500, "duration") | fields ENAME, duration
           fetched rows / total rows = 1/1
     +---------------+-------------+
     | ENAME         |   duration  |

From ba3553b984529c7b68bbaba8abf7dca87c775093 Mon Sep 17 00:00:00 2001
From: Asif Bashar <asif.bashar@gmail.com>
Date: Sat, 25 Oct 2025 20:39:16 -0700
Subject: [PATCH 18/24] requested changes

Signed-off-by: Asif Bashar <asif.bashar@gmail.com>
---
 .../opensearch/sql/calcite/CalciteRexNodeVisitor.java    | 9 +--------
 .../sql/ppl/calcite/CalcitePPLStringFunctionTest.java    | 3 +--
 2 files changed, 2 insertions(+), 10 deletions(-)

diff --git a/core/src/main/java/org/opensearch/sql/calcite/CalciteRexNodeVisitor.java b/core/src/main/java/org/opensearch/sql/calcite/CalciteRexNodeVisitor.java
index b1be49582ec..5c9057cc069 100644
--- a/core/src/main/java/org/opensearch/sql/calcite/CalciteRexNodeVisitor.java
+++ b/core/src/main/java/org/opensearch/sql/calcite/CalciteRexNodeVisitor.java
@@ -417,14 +417,7 @@ public RexNode visitFunction(Function node, CalcitePlanContext context) {
         context.setInCoalesceFunction(false);
       }
     }
-    if (node.getFuncName().equalsIgnoreCase("tostring") && args.size() == 1) {
-      RelDataType targetType =
-          context.relBuilder.getTypeFactory().createSqlType(SqlTypeName.VARCHAR);
-      // Get the source expression from arguments
-      RexNode sourceExpression = arguments.get(0);
-      // Create cast RexNode using ExtendedRexBuilder
-      return context.rexBuilder.makeCast(targetType, sourceExpression);
-    }
+
     RexNode resolvedNode =
         PPLFuncImpTable.INSTANCE.resolve(
             context.rexBuilder, node.getFuncName(), arguments.toArray(new RexNode[0]));
diff --git a/ppl/src/test/java/org/opensearch/sql/ppl/calcite/CalcitePPLStringFunctionTest.java b/ppl/src/test/java/org/opensearch/sql/ppl/calcite/CalcitePPLStringFunctionTest.java
index c06c536919c..14053bd7396 100644
--- a/ppl/src/test/java/org/opensearch/sql/ppl/calcite/CalcitePPLStringFunctionTest.java
+++ b/ppl/src/test/java/org/opensearch/sql/ppl/calcite/CalcitePPLStringFunctionTest.java
@@ -55,8 +55,7 @@ public void testToStringFormatNotSpecified() {
             + " fields string_value, cast_value";
     RelNode root = getRelNode(ppl);
     String expectedLogical =
-        "LogicalProject(string_value=[CAST($3):VARCHAR NOT NULL], cast_value=[SAFE_CAST($3)])\n"
-            + "  LogicalTableScan(table=[[scott, EMP]])\n";
+            "LogicalProject(string_value=[CAST($3):VARCHAR], cast_value=[SAFE_CAST($3)])\n  LogicalTableScan(table=[[scott, EMP]])\n";
     String expectedResult =
         "string_value=7902; cast_value=7902\n"
             + "string_value=7698; cast_value=7698\n"

From 08429c113b5846e22a0492e8568c2517de745d0b Mon Sep 17 00:00:00 2001
From: Asif Bashar <asif.bashar@gmail.com>
Date: Sat, 25 Oct 2025 20:43:07 -0700
Subject: [PATCH 19/24] requested changes

Signed-off-by: Asif Bashar <asif.bashar@gmail.com>
---
 .../java/org/opensearch/sql/calcite/CalciteRexNodeVisitor.java   | 1 -
 1 file changed, 1 deletion(-)

diff --git a/core/src/main/java/org/opensearch/sql/calcite/CalciteRexNodeVisitor.java b/core/src/main/java/org/opensearch/sql/calcite/CalciteRexNodeVisitor.java
index 5c9057cc069..bb6f16b2e8a 100644
--- a/core/src/main/java/org/opensearch/sql/calcite/CalciteRexNodeVisitor.java
+++ b/core/src/main/java/org/opensearch/sql/calcite/CalciteRexNodeVisitor.java
@@ -422,7 +422,6 @@ public RexNode visitFunction(Function node, CalcitePlanContext context) {
         PPLFuncImpTable.INSTANCE.resolve(
             context.rexBuilder, node.getFuncName(), arguments.toArray(new RexNode[0]));
     if (resolvedNode != null) {
-
       return resolvedNode;
     }
     throw new IllegalArgumentException("Unsupported operator: " + node.getFuncName());

From 7e6e9ac37610b396a29bc0a52192cc4c8ef62768 Mon Sep 17 00:00:00 2001
From: Asif Bashar <asif.bashar@gmail.com>
Date: Tue, 28 Oct 2025 09:53:01 -0700
Subject: [PATCH 20/24] updated with try catch for string parsing.

Signed-off-by: Asif Bashar <asif.bashar@gmail.com>
---
 .../sql/expression/function/udf/ToStringFunction.java     | 8 ++++++--
 .../sql/ppl/calcite/CalcitePPLStringFunctionTest.java     | 3 ++-
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/core/src/main/java/org/opensearch/sql/expression/function/udf/ToStringFunction.java b/core/src/main/java/org/opensearch/sql/expression/function/udf/ToStringFunction.java
index 46d0ada1419..e6e8dd01df0 100644
--- a/core/src/main/java/org/opensearch/sql/expression/function/udf/ToStringFunction.java
+++ b/core/src/main/java/org/opensearch/sql/expression/function/udf/ToStringFunction.java
@@ -108,7 +108,11 @@ public static String toString(int num, String format) {
 
   @Strict
   public static String toString(String str, String format) {
-    BigDecimal bd = new BigDecimal(str);
-    return toString(bd, format);
+    try {
+      BigDecimal bd = new BigDecimal(str);
+      return toString(bd, format);
+    } catch (Exception e) {
+      return null;
+    }
   }
 }
diff --git a/ppl/src/test/java/org/opensearch/sql/ppl/calcite/CalcitePPLStringFunctionTest.java b/ppl/src/test/java/org/opensearch/sql/ppl/calcite/CalcitePPLStringFunctionTest.java
index 14053bd7396..c67ba63a917 100644
--- a/ppl/src/test/java/org/opensearch/sql/ppl/calcite/CalcitePPLStringFunctionTest.java
+++ b/ppl/src/test/java/org/opensearch/sql/ppl/calcite/CalcitePPLStringFunctionTest.java
@@ -55,7 +55,8 @@ public void testToStringFormatNotSpecified() {
             + " fields string_value, cast_value";
     RelNode root = getRelNode(ppl);
     String expectedLogical =
-            "LogicalProject(string_value=[CAST($3):VARCHAR], cast_value=[SAFE_CAST($3)])\n  LogicalTableScan(table=[[scott, EMP]])\n";
+        "LogicalProject(string_value=[CAST($3):VARCHAR], cast_value=[SAFE_CAST($3)])\n"
+            + "  LogicalTableScan(table=[[scott, EMP]])\n";
     String expectedResult =
         "string_value=7902; cast_value=7902\n"
             + "string_value=7698; cast_value=7698\n"

From 1420e8fb127dbc50368d64f8a4394bb702a9aa04 Mon Sep 17 00:00:00 2001
From: Asif Bashar <asif.bashar@gmail.com>
Date: Tue, 28 Oct 2025 09:53:01 -0700
Subject: [PATCH 21/24] merge conflict fix

Signed-off-by: Asif Bashar <asif.bashar@gmail.com>
---
 docs/user/ppl/functions/conversion.rst | 83 --------------------------
 1 file changed, 83 deletions(-)

diff --git a/docs/user/ppl/functions/conversion.rst b/docs/user/ppl/functions/conversion.rst
index c9ee1576037..14f6764faf8 100644
--- a/docs/user/ppl/functions/conversion.rst
+++ b/docs/user/ppl/functions/conversion.rst
@@ -79,86 +79,3 @@ Cast function can be chained::
     | True  |
     +-------+
 
-TOSTRING
------------
-
-Description
->>>>>>>>>>>
-The following usage options are available, depending on the parameter types and the number of parameters.
-
-Usage with format type: tostring(ANY, [format]): Converts the value in first argument  to provided format type string in second argument. If second argument is not provided, then it converts to default string representation.
-Return type: string
-
-Usage for boolean parameter without format type tostring(boolean): Converts the string to 'TRUE' or 'FALSE'.
-Return type: string
-
-You can use this function with the eval commands and as part of eval expressions. If first argument can be any valid type , second argument is optional and if provided , it needs to be format name to convert to where first argument contains only numbers. If first argument is boolean, then second argument is not used even if its provided.
-
-Format types:
-
-a) "binary" Converts a number to a binary value.
-b) "hex" Converts the number to a hexadecimal value.
-c) "commas" Formats the number with commas. If the number includes a decimal, the function rounds the number to nearest two decimal places.
-d) "duration" Converts the value in seconds to the readable time format HH:MM:SS.
-e) "duration_millis" Converts the value in milliseconds to the readable time format HH:MM:SS.
-
-The format argument is optional and is only used when the value argument is a number. The tostring function supports the following formats.
-
-Basic examples:
-
-You can use this function to convert a number to a string of its binary representation.
-Example::
-
-    os> source=EMP |  eval salary_binary = tostring(SAL, "binary") | fields ENAME, salary_binary, SAL
-    fetched rows / total rows = 1/1
-    +---------------+------------------+------------+
-    | ENAME         |   salary_binary  |  SAL       |
-    |---------------+------------------+------------+
-    | SMITH         | 1001110001000000 | 80000.00   |
-    +---------------+------------------+------------+
-
-
-You can use this function to convert a number to a string of its hex representation.
-Example::
-
-    os> source=EMP |  eval salary_hex = tostring(SAL, "hex") | fields ENAME, salary_hex, SAL
-    fetched rows / total rows = 1/1
-    +---------------+---------------+------------+
-    | ENAME         |   salary_hex  |  SAL       |
-    |---------------+------------------+---------+
-    | SMITH         |   13880       | 80000.00   |
-    +---------------+---------------+------------+
-
-The following example formats the column totalSales to display values  with commas.
-Example::
-
-    os> source=EMP |  eval salary_commas = tostring(SAL, "commas") | fields ENAME, salary_commas, SAL
-     fetched rows / total rows = 1/1
-    +---------------+------------------+------------+
-    | ENAME         |   salary_commas  |  SAL       |
-    |---------------+------------------+------------+
-    | SMITH         |   80,000         | 80000.00   |
-    +---------------+------------------+------------+
-
-The following example converts number of seconds to HH:MM:SS format representing hours, minutes and seconds.
-Example::
-
-    os> source=EMP |  eval duration = tostring(6500, "duration") | fields ENAME, duration
-          fetched rows / total rows = 1/1
-    +---------------+-------------+
-    | ENAME         |   duration  |
-    |---------------+-------------+
-    | SMITH         |   01:48:20  |
-    +---------------+-------------+
-
-The following example for converts boolean parameter to string.
-Example::
-
-    os> source=people | eval `boolean_str` = tostring(1=1)| fields `boolean_str`
-    fetched rows / total rows = 1/1
-
-    +---------------------+
-    | boolean_str         |
-    |---------------------+
-    | TRUE                |
-    +---------------------+
\ No newline at end of file

From f9c9a1246eb7e6062ffab4395b120e19f2db9015 Mon Sep 17 00:00:00 2001
From: Asif Bashar <asif.bashar@gmail.com>
Date: Sat, 1 Nov 2025 21:27:04 -0700
Subject: [PATCH 22/24] added back missing tostring doc

Signed-off-by: Asif Bashar <asif.bashar@gmail.com>
---
 docs/user/ppl/functions/conversion.rst | 85 ++++++++++++++++++++++++++
 1 file changed, 85 insertions(+)

diff --git a/docs/user/ppl/functions/conversion.rst b/docs/user/ppl/functions/conversion.rst
index 849d2334e41..0f2002cff54 100644
--- a/docs/user/ppl/functions/conversion.rst
+++ b/docs/user/ppl/functions/conversion.rst
@@ -117,3 +117,88 @@ Use string in comparison operator example ::
     | True | False | True | False | True | True | null |
     +------+-------+------+-------+------+------+------+
 
+
+TOSTRING
+-----------
+
+Description
+>>>>>>>>>>>
+The following usage options are available, depending on the parameter types and the number of parameters.
+
+Usage with format type: tostring(ANY, [format]): Converts the value in first argument  to provided format type string in second argument. If second argument is not provided, then it converts to default string representation.
+Return type: string
+
+Usage for boolean parameter without format type tostring(boolean): Converts the string to 'TRUE' or 'FALSE'.
+Return type: string
+
+You can use this function with the eval commands and as part of eval expressions. If first argument can be any valid type , second argument is optional and if provided , it needs to be format name to convert to where first argument contains only numbers. If first argument is boolean, then second argument is not used even if its provided.
+
+Format types:
+
+a) "binary" Converts a number to a binary value.
+b) "hex" Converts the number to a hexadecimal value.
+c) "commas" Formats the number with commas. If the number includes a decimal, the function rounds the number to nearest two decimal places.
+d) "duration" Converts the value in seconds to the readable time format HH:MM:SS.
+e) "duration_millis" Converts the value in milliseconds to the readable time format HH:MM:SS.
+
+The format argument is optional and is only used when the value argument is a number. The tostring function supports the following formats.
+
+Basic examples:
+
+You can use this function to convert a number to a string of its binary representation.
+Example::
+
+    os> source=EMP |  eval salary_binary = tostring(SAL, "binary") | fields ENAME, salary_binary, SAL
+    fetched rows / total rows = 1/1
+    +---------------+------------------+------------+
+    | ENAME         |   salary_binary  |  SAL       |
+    |---------------+------------------+------------+
+    | SMITH         | 1001110001000000 | 80000.00   |
+    +---------------+------------------+------------+
+
+
+You can use this function to convert a number to a string of its hex representation.
+Example::
+
+    os> source=EMP |  eval salary_hex = tostring(SAL, "hex") | fields ENAME, salary_hex, SAL
+    fetched rows / total rows = 1/1
+    +---------------+---------------+------------+
+    | ENAME         |   salary_hex  |  SAL       |
+    |---------------+------------------+---------+
+    | SMITH         |   13880       | 80000.00   |
+    +---------------+---------------+------------+
+
+The following example formats the column totalSales to display values  with commas.
+Example::
+
+    os> source=EMP |  eval salary_commas = tostring(SAL, "commas") | fields ENAME, salary_commas, SAL
+     fetched rows / total rows = 1/1
+    +---------------+------------------+------------+
+    | ENAME         |   salary_commas  |  SAL       |
+    |---------------+------------------+------------+
+    | SMITH         |   80,000         | 80000.00   |
+    +---------------+------------------+------------+
+
+The following example converts number of seconds to HH:MM:SS format representing hours, minutes and seconds.
+Example::
+
+    os> source=EMP |  eval duration = tostring(6500, "duration") | fields ENAME, duration
+          fetched rows / total rows = 1/1
+    +---------------+-------------+
+    | ENAME         |   duration  |
+    |---------------+-------------+
+    | SMITH         |   01:48:20  |
+    +---------------+-------------+
+
+The following example for converts boolean parameter to string.
+Example::
+
+    os> source=people | eval `boolean_str` = tostring(1=1)| fields `boolean_str`
+    fetched rows / total rows = 1/1
+
+    +---------------------+
+    | boolean_str         |
+    |---------------------+
+    | TRUE                |
+    +---------------------+
+

From 123fcd5ddf06568e90f30d9febfa1784b746d756 Mon Sep 17 00:00:00 2001
From: Asif Bashar <asif.bashar@gmail.com>
Date: Tue, 4 Nov 2025 17:34:21 -0800
Subject: [PATCH 23/24] updated fix for doctest

Signed-off-by: Asif Bashar <asif.bashar@gmail.com>
---
 docs/user/ppl/functions/conversion.rst | 67 +++++++++++++-------------
 1 file changed, 33 insertions(+), 34 deletions(-)

diff --git a/docs/user/ppl/functions/conversion.rst b/docs/user/ppl/functions/conversion.rst
index 0f2002cff54..c5635b8509b 100644
--- a/docs/user/ppl/functions/conversion.rst
+++ b/docs/user/ppl/functions/conversion.rst
@@ -147,58 +147,57 @@ Basic examples:
 
 You can use this function to convert a number to a string of its binary representation.
 Example::
-
-    os> source=EMP |  eval salary_binary = tostring(SAL, "binary") | fields ENAME, salary_binary, SAL
+city, city.name, city.location.latitude
+    os> source=accounts |  where firstname = "Amber" |  eval balance_binary = tostring(balance, "binary") | fields firstname, balance_binary, balance
     fetched rows / total rows = 1/1
-    +---------------+------------------+------------+
-    | ENAME         |   salary_binary  |  SAL       |
-    |---------------+------------------+------------+
-    | SMITH         | 1001110001000000 | 80000.00   |
-    +---------------+------------------+------------+
+    +-------------+------------------+-----------+
+    | firstname   | balance_binary   | balance   |
+    |-------------+------------------+-----------|
+    | Amber       | 1001100100111001 | 39225     |
+    +-------------+------------------+-----------+
 
 
 You can use this function to convert a number to a string of its hex representation.
 Example::
 
-    os> source=EMP |  eval salary_hex = tostring(SAL, "hex") | fields ENAME, salary_hex, SAL
+    os> source=accounts |  where firstname = "Amber" |  eval balance_hex = tostring(balance, "hex") | fields firstname, balance_hex, balance
     fetched rows / total rows = 1/1
-    +---------------+---------------+------------+
-    | ENAME         |   salary_hex  |  SAL       |
-    |---------------+------------------+---------+
-    | SMITH         |   13880       | 80000.00   |
-    +---------------+---------------+------------+
+    +-------------+---------------+-----------+
+    | firstname   | balance_hex   | balance   |
+    |-------------+---------------+-----------|
+    | Amber       | 9939          | 39225     |
+    +-------------+---------------+-----------+
 
 The following example formats the column totalSales to display values  with commas.
 Example::
 
-    os> source=EMP |  eval salary_commas = tostring(SAL, "commas") | fields ENAME, salary_commas, SAL
-     fetched rows / total rows = 1/1
-    +---------------+------------------+------------+
-    | ENAME         |   salary_commas  |  SAL       |
-    |---------------+------------------+------------+
-    | SMITH         |   80,000         | 80000.00   |
-    +---------------+------------------+------------+
+    os> source=accounts |  where firstname = "Amber" |  eval balance_commas = tostring(balance, "commas") | fields firstname, balance_commas, balance
+    fetched rows / total rows = 1/1
+    +-------------+------------------+-----------+
+    | firstname   | balance_commas   | balance   |
+    |-------------+------------------+-----------|
+    | Amber       | 39,225           | 39225     |
+    +-------------+------------------+-----------+
 
 The following example converts number of seconds to HH:MM:SS format representing hours, minutes and seconds.
 Example::
 
-    os> source=EMP |  eval duration = tostring(6500, "duration") | fields ENAME, duration
-          fetched rows / total rows = 1/1
-    +---------------+-------------+
-    | ENAME         |   duration  |
-    |---------------+-------------+
-    | SMITH         |   01:48:20  |
-    +---------------+-------------+
+    os> source=accounts |  where firstname = "Amber" | eval duration = tostring(6500, "duration") | fields firstname, duration
+    fetched rows / total rows = 1/1
+    +-------------+------------+
+    | firstname   | duration   |
+    |-------------+------------|
+    | Amber       | 01:48:20   |
+    +-------------+------------+
 
 The following example for converts boolean parameter to string.
 Example::
 
-    os> source=people | eval `boolean_str` = tostring(1=1)| fields `boolean_str`
+    os> source=accounts |  where firstname = "Amber"| eval `boolean_str` = tostring(1=1)| fields `boolean_str`
     fetched rows / total rows = 1/1
-
-    +---------------------+
-    | boolean_str         |
-    |---------------------+
-    | TRUE                |
-    +---------------------+
+    +---------------+
+    | boolean_str   |
+    |---------------|
+    | TRUE          |
+    +---------------+
 

From e6d0c8c80772fa9138c8919d6ccb06954703ac24 Mon Sep 17 00:00:00 2001
From: Asif Bashar <asif.bashar@gmail.com>
Date: Wed, 5 Nov 2025 09:27:45 -0800
Subject: [PATCH 24/24] fix doctest failures

Signed-off-by: Asif Bashar <asif.bashar@gmail.com>
---
 docs/user/ppl/functions/conversion.rst | 50 +++++++++++++-------------
 1 file changed, 25 insertions(+), 25 deletions(-)

diff --git a/docs/user/ppl/functions/conversion.rst b/docs/user/ppl/functions/conversion.rst
index c5635b8509b..82d760cc3ce 100644
--- a/docs/user/ppl/functions/conversion.rst
+++ b/docs/user/ppl/functions/conversion.rst
@@ -150,11 +150,11 @@ Example::
 city, city.name, city.location.latitude
     os> source=accounts |  where firstname = "Amber" |  eval balance_binary = tostring(balance, "binary") | fields firstname, balance_binary, balance
     fetched rows / total rows = 1/1
-    +-------------+------------------+-----------+
-    | firstname   | balance_binary   | balance   |
-    |-------------+------------------+-----------|
-    | Amber       | 1001100100111001 | 39225     |
-    +-------------+------------------+-----------+
+    +-----------+------------------+---------+
+    | firstname | balance_binary   | balance |
+    |-----------+------------------+---------|
+    | Amber     | 1001100100111001 | 39225   |
+    +-----------+------------------+---------+
 
 
 You can use this function to convert a number to a string of its hex representation.
@@ -162,42 +162,42 @@ Example::
 
     os> source=accounts |  where firstname = "Amber" |  eval balance_hex = tostring(balance, "hex") | fields firstname, balance_hex, balance
     fetched rows / total rows = 1/1
-    +-------------+---------------+-----------+
-    | firstname   | balance_hex   | balance   |
-    |-------------+---------------+-----------|
-    | Amber       | 9939          | 39225     |
-    +-------------+---------------+-----------+
+    +-----------+-------------+---------+
+    | firstname | balance_hex | balance |
+    |-----------+-------------+---------|
+    | Amber     | 9939        | 39225   |
+    +-----------+-------------+---------+
 
 The following example formats the column totalSales to display values  with commas.
 Example::
 
     os> source=accounts |  where firstname = "Amber" |  eval balance_commas = tostring(balance, "commas") | fields firstname, balance_commas, balance
     fetched rows / total rows = 1/1
-    +-------------+------------------+-----------+
-    | firstname   | balance_commas   | balance   |
-    |-------------+------------------+-----------|
-    | Amber       | 39,225           | 39225     |
-    +-------------+------------------+-----------+
+    +-----------+----------------+---------+
+    | firstname | balance_commas | balance |
+    |-----------+----------------+---------|
+    | Amber     | 39,225         | 39225   |
+    +-----------+----------------+---------+
 
 The following example converts number of seconds to HH:MM:SS format representing hours, minutes and seconds.
 Example::
 
     os> source=accounts |  where firstname = "Amber" | eval duration = tostring(6500, "duration") | fields firstname, duration
     fetched rows / total rows = 1/1
-    +-------------+------------+
-    | firstname   | duration   |
-    |-------------+------------|
-    | Amber       | 01:48:20   |
-    +-------------+------------+
+    +-----------+----------+
+    | firstname | duration |
+    |-----------+----------|
+    | Amber     | 01:48:20 |
+    +-----------+----------+
 
 The following example for converts boolean parameter to string.
 Example::
 
     os> source=accounts |  where firstname = "Amber"| eval `boolean_str` = tostring(1=1)| fields `boolean_str`
     fetched rows / total rows = 1/1
-    +---------------+
-    | boolean_str   |
-    |---------------|
-    | TRUE          |
-    +---------------+
+    +-------------+
+    | boolean_str |
+    |-------------|
+    | TRUE        |
+    +-------------+