diff --git a/docs/user/ppl/functions/math.rst b/docs/user/ppl/functions/math.rst
index 2944f3fb8dc..b2b0dd47415 100644
--- a/docs/user/ppl/functions/math.rst
+++ b/docs/user/ppl/functions/math.rst
@@ -132,6 +132,84 @@ Example::
     +--------------+
 
 
+SUM
+---
+
+Description
+>>>>>>>>>>>
+
+Usage: sum(x, y, ...) calculates the sum of all provided arguments. This function accepts a variable number of arguments.
+
+Note: This function is only available in the eval command context and is rewritten to arithmetic addition while query parsing.
+
+Argument type: Variable number of INTEGER/LONG/FLOAT/DOUBLE arguments
+
+Return type: Wider number type among all arguments
+
+Example::
+
+    os> source=accounts | eval `SUM(1, 2, 3)` = SUM(1, 2, 3) | fields `SUM(1, 2, 3)`
+    fetched rows / total rows = 4/4
+    +--------------+
+    | SUM(1, 2, 3) |
+    |--------------|
+    | 6            |
+    | 6            |
+    | 6            |
+    | 6            |
+    +--------------+
+
+    os> source=accounts | eval total = SUM(age, 10, 5) | fields age, total
+    fetched rows / total rows = 4/4
+    +-----+-------+
+    | age | total |
+    |-----+-------|
+    | 32  | 47    |
+    | 36  | 51    |
+    | 28  | 43    |
+    | 33  | 48    |
+    +-----+-------+
+
+
+AVG
+---
+
+Description
+>>>>>>>>>>>
+
+Usage: avg(x, y, ...) calculates the average (arithmetic mean) of all provided arguments. This function accepts a variable number of arguments.
+
+Note: This function is only available in the eval command context and is rewritten to arithmetic expression (sum / count) at query parsing time.
+
+Argument type: Variable number of INTEGER/LONG/FLOAT/DOUBLE arguments
+
+Return type: DOUBLE
+
+Example::
+
+    os> source=accounts | eval `AVG(1, 2, 3)` = AVG(1, 2, 3) | fields `AVG(1, 2, 3)`
+    fetched rows / total rows = 4/4
+    +--------------+
+    | AVG(1, 2, 3) |
+    |--------------|
+    | 2.0          |
+    | 2.0          |
+    | 2.0          |
+    | 2.0          |
+    +--------------+
+
+    os> source=accounts | eval average = AVG(age, 30) | fields age, average
+    fetched rows / total rows = 4/4
+    +-----+---------+
+    | age | average |
+    |-----+---------|
+    | 32  | 31.0    |
+    | 36  | 33.0    |
+    | 28  | 29.0    |
+    | 33  | 31.5    |
+    +-----+---------+
+
+
 ACOS
 ----
 
diff --git a/integ-test/src/test/java/org/opensearch/sql/ppl/MathematicalFunctionIT.java b/integ-test/src/test/java/org/opensearch/sql/ppl/MathematicalFunctionIT.java
index f53049fb5c3..6cd5063b5a0 100644
--- a/integ-test/src/test/java/org/opensearch/sql/ppl/MathematicalFunctionIT.java
+++ b/integ-test/src/test/java/org/opensearch/sql/ppl/MathematicalFunctionIT.java
@@ -547,4 +547,225 @@ public void testRint() throws IOException {
     verifySchema(result, schema("f", null, "double"));
     verifySome(result.getJSONArray("datarows"), rows(Math.rint(1.7)));
   }
+
+  // SUM function tests for eval command
+  @Test
+  public void testEvalSumSingleInteger() throws IOException {
+    JSONObject result =
+        executeQuery(
+            String.format("source=%s | eval f = sum(42) | fields f | head 5", TEST_INDEX_BANK));
+    verifySchema(result, schema("f", null, "int"));
+    verifyDataRows(result, rows(42), rows(42), rows(42), rows(42), rows(42));
+  }
+
+  @Test
+  public void testEvalSumMultipleIntegers() throws IOException {
+    JSONObject result =
+        executeQuery(
+            String.format(
+                "source=%s | eval f = sum(1, 2, 3) | fields f | head 5", TEST_INDEX_BANK));
+    verifySchema(result, schema("f", null, "int"));
+    verifyDataRows(result, rows(6), rows(6), rows(6), rows(6), rows(6));
+  }
+
+  @Test
+  public void testEvalSumMixedNumericTypes() throws IOException {
+    JSONObject result =
+        executeQuery(
+            String.format("source=%s | eval f = sum(1, 2.5) | fields f | head 5", TEST_INDEX_BANK));
+    verifySchema(result, schema("f", null, "double"));
+    verifyDataRows(result, rows(3.5), rows(3.5), rows(3.5), rows(3.5), rows(3.5));
+  }
+
+  @Test
+  public void testEvalSumWithFields() throws IOException {
+    JSONObject result =
+        executeQuery(
+            String.format(
+                "source=%s | eval f = sum(age, 10) | fields f | head 7", TEST_INDEX_BANK));
+    verifySchema(result, schema("f", null, "int"));
+    verifyDataRows(result, rows(42), rows(46), rows(38), rows(43), rows(46), rows(49), rows(44));
+  }
+
+  @Test
+  public void testEvalSumMultipleNumericArguments() throws IOException {
+    JSONObject result =
+        executeQuery(
+            String.format(
+                "source=%s | eval f = sum(1, 2, 3, 4, 5) | fields f | head 5", TEST_INDEX_BANK));
+    verifySchema(result, schema("f", null, "int"));
+    verifyDataRows(result, rows(15), rows(15), rows(15), rows(15), rows(15));
+  }
+
+  // AVG function tests for eval command
+  @Test
+  public void testEvalAvgSingleInteger() throws IOException {
+    JSONObject result =
+        executeQuery(
+            String.format("source=%s | eval f = avg(42) | fields f | head 5", TEST_INDEX_BANK));
+    verifySchema(result, schema("f", null, "double"));
+    verifyDataRows(result, rows(42.0), rows(42.0), rows(42.0), rows(42.0), rows(42.0));
+  }
+
+  @Test
+  public void testEvalAvgMultipleIntegers() throws IOException {
+    JSONObject result =
+        executeQuery(
+            String.format(
+                "source=%s | eval f = avg(1, 2, 3) | fields f | head 5", TEST_INDEX_BANK));
+    verifySchema(result, schema("f", null, "double"));
+    verifyDataRows(result, rows(2.0), rows(2.0), rows(2.0), rows(2.0), rows(2.0));
+  }
+
+  @Test
+  public void testEvalAvgTwoIntegers() throws IOException {
+    JSONObject result =
+        executeQuery(
+            String.format("source=%s | eval f = avg(1, 2) | fields f | head 5", TEST_INDEX_BANK));
+    verifySchema(result, schema("f", null, "double"));
+    verifyDataRows(result, rows(1.5), rows(1.5), rows(1.5), rows(1.5), rows(1.5));
+  }
+
+  @Test
+  public void testEvalAvgMixedNumericTypes() throws IOException {
+    JSONObject result =
+        executeQuery(
+            String.format("source=%s | eval f = avg(1, 2.5) | fields f | head 5", TEST_INDEX_BANK));
+    verifySchema(result, schema("f", null, "double"));
+    verifyDataRows(result, rows(1.75), rows(1.75), rows(1.75), rows(1.75), rows(1.75));
+  }
+
+  @Test
+  public void testEvalAvgWithFields() throws IOException {
+    JSONObject result =
+        executeQuery(
+            String.format(
+                "source=%s | eval f = avg(age, 10) | fields f | head 7", TEST_INDEX_BANK));
+    verifySchema(result, schema("f", null, "double"));
+    verifyDataRows(
+        result, rows(21.0), rows(23.0), rows(19.0), rows(21.5), rows(23.0), rows(24.5), rows(22.0));
+  }
+
+  @Test
+  public void testEvalAvgMultipleValues() throws IOException {
+    JSONObject result =
+        executeQuery(
+            String.format("source=%s | eval f = avg(1, 4) | fields f | head 5", TEST_INDEX_BANK));
+    verifySchema(result, schema("f", null, "double"));
+    verifyDataRows(result, rows(2.5), rows(2.5), rows(2.5), rows(2.5), rows(2.5));
+  }
+
+  @Test
+  public void testEvalAvgFiveValues() throws IOException {
+    JSONObject result =
+        executeQuery(
+            String.format(
+                "source=%s | eval f = avg(1, 2, 3, 4, 5) | fields f | head 5", TEST_INDEX_BANK));
+    verifySchema(result, schema("f", null, "double"));
+    verifyDataRows(result, rows(3.0), rows(3.0), rows(3.0), rows(3.0), rows(3.0));
+  }
+
+  // Combined sum and avg tests
+  @Test
+  public void testEvalSumAndAvgComparison() throws IOException {
+    JSONObject result =
+        executeQuery(
+            String.format(
+                "source=%s | eval sum_val = sum(10, 20, 30), avg_val = avg(10, 20, 30) | fields"
+                    + " sum_val, avg_val | head 5",
+                TEST_INDEX_BANK));
+    verifySchema(result, schema("sum_val", null, "int"), schema("avg_val", null, "double"));
+    verifyDataRows(
+        result, rows(60, 20.0), rows(60, 20.0), rows(60, 20.0), rows(60, 20.0), rows(60, 20.0));
+  }
+
+  @Test
+  public void testEvalSumInWhereClause() throws IOException {
+    JSONObject result =
+        executeQuery(
+            String.format(
+                "source=%s | where sum(age, 10) > 40 | eval f = sum(age, 10) | fields f | head 6",
+                TEST_INDEX_BANK));
+    verifySchema(result, schema("f", null, "int"));
+    // Should return rows where age + 10 > 40, so age > 30
+    verifyDataRows(result, rows(42), rows(46), rows(43), rows(46), rows(49), rows(44));
+  }
+
+  @Test
+  public void testEvalAvgInWhereClause() throws IOException {
+    JSONObject result =
+        executeQuery(
+            String.format(
+                "source=%s | where avg(age, 10) > 20 | eval f = avg(age, 10) | fields f | head 6",
+                TEST_INDEX_BANK));
+    verifySchema(result, schema("f", null, "double"));
+    // Should return rows where (age + 10) / 2 > 20, so age > 30
+    verifyDataRows(result, rows(21.0), rows(23.0), rows(21.5), rows(23.0), rows(24.5), rows(22.0));
+  }
+
+  @Test
+  public void testEvalComplexExpression() throws IOException {
+    JSONObject result =
+        executeQuery(
+            String.format(
+                "source=%s | eval f = sum(age, 5) + avg(10, 20) | fields f | head 5",
+                TEST_INDEX_BANK));
+    verifySchema(result, schema("f", null, "double"));
+    // sum(age, 5) + avg(10, 20) = (age + 5) + 15.0
+    verifyDataRows(result, rows(52.0), rows(56.0), rows(48.0), rows(53.0), rows(56.0));
+  }
+
+  @Test
+  public void testEvalNestedSumAvg() throws IOException {
+    // Note: This tests the arithmetic expression rewriting, not actual nested function calls
+    JSONObject result =
+        executeQuery(
+            String.format(
+                "source=%s | eval f = sum(avg(20, 30), 10) | fields f | head 5", TEST_INDEX_BANK));
+    verifySchema(result, schema("f", null, "double"));
+    // avg(20, 30) = 25.0, sum(25.0, 10) = 35.0
+    verifyDataRows(result, rows(35.0), rows(35.0), rows(35.0), rows(35.0), rows(35.0));
+  }
+
+  @Test
+  public void testEvalSumWithMultipleFields() throws IOException {
+    JSONObject result =
+        executeQuery(
+            String.format(
+                "source=%s | eval f = sum(age, age, 10) | fields f | head 5", TEST_INDEX_BANK));
+    verifySchema(result, schema("f", null, "int"));
+    // sum(age, age, 10) = age + age + 10 = 2*age + 10
+    verifyDataRows(result, rows(74), rows(82), rows(66), rows(76), rows(82));
+  }
+
+  @Test
+  public void testEvalAvgWithExpression() throws IOException {
+    JSONObject result =
+        executeQuery(
+            String.format(
+                "source=%s | eval f = avg(age * 2, 10) | fields f | head 5", TEST_INDEX_BANK));
+    verifySchema(result, schema("f", null, "double"));
+    // avg(age * 2, 10) = (age * 2 + 10) / 2 = age + 5
+    verifyDataRows(result, rows(37.0), rows(41.0), rows(33.0), rows(38.0), rows(41.0));
+  }
+
+  @Test
+  public void testEvalSumWithNegativeNumbers() throws IOException {
+    JSONObject result =
+        executeQuery(
+            String.format(
+                "source=%s | eval f = sum(-5, 10, -3) | fields f | head 5", TEST_INDEX_BANK));
+    verifySchema(result, schema("f", null, "int"));
+    verifyDataRows(result, rows(2), rows(2), rows(2), rows(2), rows(2));
+  }
+
+  @Test
+  public void testEvalAvgWithNegativeNumbers() throws IOException {
+    JSONObject result =
+        executeQuery(
+            String.format(
+                "source=%s | eval f = avg(-10, 10) | fields f | head 5", TEST_INDEX_BANK));
+    verifySchema(result, schema("f", null, "double"));
+    verifyDataRows(result, rows(0.0), rows(0.0), rows(0.0), rows(0.0), rows(0.0));
+  }
 }
diff --git a/ppl/src/main/antlr/OpenSearchPPLParser.g4 b/ppl/src/main/antlr/OpenSearchPPLParser.g4
index 2699d7c31e1..2221a36da43 100644
--- a/ppl/src/main/antlr/OpenSearchPPLParser.g4
+++ b/ppl/src/main/antlr/OpenSearchPPLParser.g4
@@ -710,6 +710,8 @@ mathematicalFunctionName
    | TRUNCATE
    | RINT
    | SIGNUM
+   | SUM
+   | AVG
    | trigonometricFunctionName
    ;
 
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 1170123f69d..5e865fe7333 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
@@ -5,9 +5,7 @@
 
 package org.opensearch.sql.ppl.parser;
 
-import static org.opensearch.sql.expression.function.BuiltinFunctionName.IS_NOT_NULL;
-import static org.opensearch.sql.expression.function.BuiltinFunctionName.IS_NULL;
-import static org.opensearch.sql.expression.function.BuiltinFunctionName.POSITION;
+import static org.opensearch.sql.expression.function.BuiltinFunctionName.*;
 import static org.opensearch.sql.ppl.antlr.parser.OpenSearchPPLParser.BinaryArithmeticContext;
 import static org.opensearch.sql.ppl.antlr.parser.OpenSearchPPLParser.BooleanLiteralContext;
 import static org.opensearch.sql.ppl.antlr.parser.OpenSearchPPLParser.BySpanClauseContext;
@@ -271,9 +269,16 @@ public UnresolvedExpression visitCaseFunctionCall(
   @Override
   public UnresolvedExpression visitEvalFunctionCall(EvalFunctionCallContext ctx) {
     final String functionName = ctx.evalFunctionName().getText();
-    return buildFunction(
-        FUNCTION_NAME_MAPPING.getOrDefault(functionName.toLowerCase(Locale.ROOT), functionName),
-        ctx.functionArgs().functionArg());
+    final String mappedName =
+        FUNCTION_NAME_MAPPING.getOrDefault(functionName.toLowerCase(Locale.ROOT), functionName);
+
+    // Rewrite sum and avg functions to arithmetic expressions
+    if (SUM.getName().getFunctionName().equalsIgnoreCase(mappedName)
+        || AVG.getName().getFunctionName().equalsIgnoreCase(mappedName)) {
+      return rewriteSumAvgFunction(mappedName, ctx.functionArgs().functionArg());
+    }
+
+    return buildFunction(mappedName, ctx.functionArgs().functionArg());
   }
 
   /** Cast function. */
@@ -293,6 +298,55 @@ private Function buildFunction(
         functionName, args.stream().map(this::visitFunctionArg).collect(Collectors.toList()));
   }
 
+  /**
+   * Rewrites sum(a, b, c, ...) to (a + b + c + ...) and avg(a, b, c, ...) to (a + b + c + ...) / n
+   * Uses balanced tree construction to avoid deep recursion with large argument lists.
+   */
+  private UnresolvedExpression rewriteSumAvgFunction(
+      String functionName, List<OpenSearchPPLParser.FunctionArgContext> args) {
+    if (args.isEmpty()) {
+      throw new SyntaxCheckException(functionName + " function requires at least one argument");
+    }
+
+    List<UnresolvedExpression> arguments =
+        args.stream().map(this::visitFunctionArg).collect(Collectors.toList());
+
+    // Build the sum expression as a balanced tree to avoid deep recursion
+    UnresolvedExpression functionExpr = buildBalancedTree("+", arguments);
+
+    // For avg, divide by the count of arguments
+    if (AVG.getName().getFunctionName().equalsIgnoreCase(functionName)) {
+      UnresolvedExpression count = AstDSL.doubleLiteral((double) arguments.size());
+      functionExpr = new Function("/", Arrays.asList(functionExpr, count));
+    }
+
+    return functionExpr;
+  }
+
+  /**
+   * Builds a balanced tree of binary operations to avoid deep recursion. For example, [a, b, c, d]
+   * becomes ((a + b) + (c + d)) instead of (((a + b) + c) + d). This ensures recursion depth is
+   * O(log n) instead of O(n).
+   */
+  private UnresolvedExpression buildBalancedTree(
+      String operator, List<UnresolvedExpression> expressions) {
+    if (expressions.size() == 1) {
+      return expressions.get(0);
+    }
+
+    if (expressions.size() == 2) {
+      return new Function(operator, Arrays.asList(expressions.get(0), expressions.get(1)));
+    }
+
+    // Split the list in half and recursively build balanced subtrees
+    int mid = expressions.size() / 2;
+    UnresolvedExpression left = buildBalancedTree(operator, expressions.subList(0, mid));
+    UnresolvedExpression right =
+        buildBalancedTree(operator, expressions.subList(mid, expressions.size()));
+
+    return new Function(operator, Arrays.asList(left, right));
+  }
+
   @Override
   public UnresolvedExpression visitSingleFieldRelevanceFunction(
       SingleFieldRelevanceFunctionContext ctx) {
diff --git a/ppl/src/test/java/org/opensearch/sql/ppl/calcite/CalcitePPLEvalTest.java b/ppl/src/test/java/org/opensearch/sql/ppl/calcite/CalcitePPLEvalTest.java
index db759a7b9af..e09b62b748a 100644
--- a/ppl/src/test/java/org/opensearch/sql/ppl/calcite/CalcitePPLEvalTest.java
+++ b/ppl/src/test/java/org/opensearch/sql/ppl/calcite/CalcitePPLEvalTest.java
@@ -98,6 +98,73 @@ public void testEval3() {
     verifyPPLToSparkSQL(root, expectedSparkSql);
   }
 
+  @Test
+  public void testEvalSum() {
+    String ppl = "source=EMP | eval total = sum(1, 2, 3) | fields EMPNO, total";
+    RelNode root = getRelNode(ppl);
+    String expectedLogical =
+        "LogicalProject(EMPNO=[$0], total=[+(1, +(2, 3))])\n"
+            + "  LogicalTableScan(table=[[scott, EMP]])\n";
+    verifyLogical(root, expectedLogical);
+
+    String expectedSparkSql = "SELECT `EMPNO`, 1 + (2 + 3) `total`\n" + "FROM `scott`.`EMP`";
+    verifyPPLToSparkSQL(root, expectedSparkSql);
+  }
+
+  @Test
+  public void testEvalSumWithFields() {
+    String ppl = "source=EMP | eval total = sum(SAL, COMM, 100) | fields EMPNO, total";
+    RelNode root = getRelNode(ppl);
+    String expectedLogical =
+        "LogicalProject(EMPNO=[$0], total=[+($5, +($6, 100))])\n"
+            + "  LogicalTableScan(table=[[scott, EMP]])\n";
+    verifyLogical(root, expectedLogical);
+
+    String expectedSparkSql =
+        "SELECT `EMPNO`, `SAL` + (`COMM` + 100) `total`\n" + "FROM `scott`.`EMP`";
+    verifyPPLToSparkSQL(root, expectedSparkSql);
+  }
+
+  @Test
+  public void testEvalAvg() {
+    String ppl = "source=EMP | eval average = avg(10, 20, 30) | fields EMPNO, average";
+    RelNode root = getRelNode(ppl);
+    String expectedLogical =
+        "LogicalProject(EMPNO=[$0], average=[DIVIDE(+(10, +(20, 30)), 3.0E0:DOUBLE)])\n"
+            + "  LogicalTableScan(table=[[scott, EMP]])\n";
+    verifyLogical(root, expectedLogical);
+
+    String expectedSparkSql =
+        "SELECT `EMPNO`, `DIVIDE`(10 + (20 + 30), 3.0E0) `average`\n" + "FROM `scott`.`EMP`";
+    verifyPPLToSparkSQL(root, expectedSparkSql);
+  }
+
+  @Test
+  public void testEvalAvgWithFields() {
+    String ppl = "source=EMP | eval avgSal = avg(SAL, COMM) | fields EMPNO, avgSal";
+    RelNode root = getRelNode(ppl);
+    String expectedLogical =
+        "LogicalProject(EMPNO=[$0], avgSal=[DIVIDE(+($5, $6), 2.0E0:DOUBLE)])\n"
+            + "  LogicalTableScan(table=[[scott, EMP]])\n";
+    verifyLogical(root, expectedLogical);
+
+    String expectedSparkSql =
+        "SELECT `EMPNO`, `DIVIDE`(`SAL` + `COMM`, 2.0E0) `avgSal`\n" + "FROM `scott`.`EMP`";
+    verifyPPLToSparkSQL(root, expectedSparkSql);
+  }
+
+  @Test
+  public void testEvalSumSingleArg() {
+    String ppl = "source=EMP | eval total = sum(42) | fields EMPNO, total";
+    RelNode root = getRelNode(ppl);
+    String expectedLogical =
+        "LogicalProject(EMPNO=[$0], total=[42])\n" + "  LogicalTableScan(table=[[scott, EMP]])\n";
+    verifyLogical(root, expectedLogical);
+
+    String expectedSparkSql = "SELECT `EMPNO`, 42 `total`\n" + "FROM `scott`.`EMP`";
+    verifyPPLToSparkSQL(root, expectedSparkSql);
+  }
+
   @Test
   public void testEvalWithSort() {
     String ppl = "source=EMP | eval a = EMPNO | sort - a | fields a";
diff --git a/ppl/src/test/java/org/opensearch/sql/ppl/parser/AstExpressionBuilderTest.java b/ppl/src/test/java/org/opensearch/sql/ppl/parser/AstExpressionBuilderTest.java
index ca0f508823f..52c1c8885fa 100644
--- a/ppl/src/test/java/org/opensearch/sql/ppl/parser/AstExpressionBuilderTest.java
+++ b/ppl/src/test/java/org/opensearch/sql/ppl/parser/AstExpressionBuilderTest.java
@@ -604,6 +604,174 @@ public void testDataTypeFuncCall() {
         eval(relation("t"), let(field("f"), cast(intLiteral(1), stringLiteral("string")))));
   }
 
+  @Test
+  public void testEvalSumFunctionSingleArg() {
+    // sum(42) -> 42
+    assertEqual("source=t | eval f=sum(42)", eval(relation("t"), let(field("f"), intLiteral(42))));
+  }
+
+  @Test
+  public void testEvalSumFunctionMultipleArgs() {
+    // sum(1, 2, 3) -> (1 + (2 + 3)) - balanced tree
+    assertEqual(
+        "source=t | eval f=sum(1, 2, 3)",
+        eval(
+            relation("t"),
+            let(
+                field("f"),
+                function("+", intLiteral(1), function("+", intLiteral(2), intLiteral(3))))));
+  }
+
+  @Test
+  public void testEvalSumFunctionWithFields() {
+    // sum(a, b, 10) -> (a + (b + 10)) - balanced tree
+    assertEqual(
+        "source=t | eval f=sum(a, b, 10)",
+        eval(
+            relation("t"),
+            let(field("f"), function("+", field("a"), function("+", field("b"), intLiteral(10))))));
+  }
+
+  @Test
+  public void testEvalSumFunctionFourArgs() {
+    // sum(1, 2, 3, 4) -> ((1 + 2) + (3 + 4)) - balanced tree
+    assertEqual(
+        "source=t | eval f=sum(1, 2, 3, 4)",
+        eval(
+            relation("t"),
+            let(
+                field("f"),
+                function(
+                    "+",
+                    function("+", intLiteral(1), intLiteral(2)),
+                    function("+", intLiteral(3), intLiteral(4))))));
+  }
+
+  @Test
+  public void testEvalSumFunctionMixedTypes() {
+    // sum(1, 2.5) -> (1 + 2.5)
+    assertEqual(
+        "source=t | eval f=sum(1, 2.5)",
+        eval(relation("t"), let(field("f"), function("+", intLiteral(1), decimalLiteral(2.5)))));
+  }
+
+  @Test
+  public void testEvalAvgFunctionSingleArg() {
+    // avg(42) -> 42 / 1.0
+    assertEqual(
+        "source=t | eval f=avg(42)",
+        eval(relation("t"), let(field("f"), function("/", intLiteral(42), doubleLiteral(1.0)))));
+  }
+
+  @Test
+  public void testEvalAvgFunctionTwoArgs() {
+    // avg(10, 20) -> (10 + 20) / 2.0
+    assertEqual(
+        "source=t | eval f=avg(10, 20)",
+        eval(
+            relation("t"),
+            let(
+                field("f"),
+                function("/", function("+", intLiteral(10), intLiteral(20)), doubleLiteral(2.0)))));
+  }
+
+  @Test
+  public void testEvalAvgFunctionMultipleArgs() {
+    // avg(1, 2, 3) -> (1 + (2 + 3)) / 3.0 - balanced tree
+    assertEqual(
+        "source=t | eval f=avg(1, 2, 3)",
+        eval(
+            relation("t"),
+            let(
+                field("f"),
+                function(
+                    "/",
+                    function("+", intLiteral(1), function("+", intLiteral(2), intLiteral(3))),
+                    doubleLiteral(3.0)))));
+  }
+
+  @Test
+  public void testEvalAvgFunctionWithFields() {
+    // avg(a, b) -> (a + b) / 2.0
+    assertEqual(
+        "source=t | eval f=avg(a, b)",
+        eval(
+            relation("t"),
+            let(
+                field("f"),
+                function("/", function("+", field("a"), field("b")), doubleLiteral(2.0)))));
+  }
+
+  @Test
+  public void testEvalAvgFunctionMixedTypes() {
+    // avg(1, 2.5, 3) -> (1 + (2.5 + 3)) / 3.0 - balanced tree
+    assertEqual(
+        "source=t | eval f=avg(1, 2.5, 3)",
+        eval(
+            relation("t"),
+            let(
+                field("f"),
+                function(
+                    "/",
+                    function("+", intLiteral(1), function("+", decimalLiteral(2.5), intLiteral(3))),
+                    doubleLiteral(3.0)))));
+  }
+
+  @Test
+  public void testEvalComplexExpressionWithSumAndAvg() {
+    // sum(a, 5) + avg(10, 20) -> (a + 5) + ((10 + 20) / 2.0)
+    assertEqual(
+        "source=t | eval f=sum(a, 5) + avg(10, 20)",
+        eval(
+            relation("t"),
+            let(
+                field("f"),
+                function(
+                    "+",
+                    function("+", field("a"), intLiteral(5)),
+                    function(
+                        "/", function("+", intLiteral(10), intLiteral(20)), doubleLiteral(2.0))))));
+  }
+
+  @Test
+  public void testWhereSumFunction() {
+    // where sum(a, 10) > 20 -> where (a + 10) > 20
+    assertEqual(
+        "source=t | where sum(a, 10) > 20",
+        filter(
+            relation("t"),
+            compare(">", function("+", field("a"), intLiteral(10)), intLiteral(20))));
+  }
+
+  @Test
+  public void testWhereAvgFunction() {
+    // where avg(a, b) < 15.5 -> where (a + b) / 2.0 < 15.5
+    assertEqual(
+        "source=t | where avg(a, b) < 15.5",
+        filter(
+            relation("t"),
+            compare(
+                "<",
+                function("/", function("+", field("a"), field("b")), doubleLiteral(2.0)),
+                decimalLiteral(15.5))));
+  }
+
+  @Test
+  public void testWhereSumAndAvgComparison() {
+    // where sum(a, b) > avg(10, 20, 30) -> where (a + b) > (10 + (20 + 30)) / 3.0 - balanced tree
+    assertEqual(
+        "source=t | where sum(a, b) > avg(10, 20, 30)",
+        filter(
+            relation("t"),
+            compare(
+                ">",
+                function("+", field("a"), field("b")),
+                function(
+                    "/",
+                    function("+", intLiteral(10), function("+", intLiteral(20), intLiteral(30))),
+                    doubleLiteral(3.0)))));
+  }
+
   @Test
   public void testNestedFieldName() {
     assertEqual(