Remove named function arg from functions other than table functions

Signed-off-by: Yuanchun Shen <yuanchu@amazon.com>

Author: yuancu

ppl/src/main/antlr/OpenSearchPPLParser.g4

@@ -518,7 +518,7 @@ tableSource
    ;
 
 tableFunction
-   : qualifiedName LT_PRTHS functionArgs RT_PRTHS
+   : qualifiedName LT_PRTHS namedFunctionArgs RT_PRTHS
    ;
 
 // fields
@@ -593,10 +593,17 @@ functionArgs
    : (functionArg (COMMA functionArg)*)?
    ;
 
+namedFunctionArgs
+   : (namedFunctionArg (COMMA namedFunctionArg)*)?
+   ;
+
 functionArg
-   : (ident EQUAL)? functionArgExpression
+   : functionArgExpression
    ;
 
+namedFunctionArg
+   : (ident EQUAL)? functionArgExpression
+   ;
 
 functionArgExpression
    : lambda

ppl/src/main/java/org/opensearch/sql/ppl/parser/AstBuilder.java

@@ -551,8 +551,8 @@ public UnresolvedPlan visitTableSourceClause(TableSourceClauseContext ctx) {
   @Override
   public UnresolvedPlan visitTableFunction(TableFunctionContext ctx) {
     ImmutableList.Builder<UnresolvedExpression> builder = ImmutableList.builder();
-    ctx.functionArgs()
-        .functionArg()
+    ctx.namedFunctionArgs()
+        .namedFunctionArg()
         .forEach(
             arg -> {
               String argName = (arg.ident() != null) ? arg.ident().getText() : null;