Add PARTITION BY support in OVER clause for window functions

- Add Partitions and OrderByClause fields to OverClause AST type
- Update OVER clause parser to handle PARTITION BY and ORDER BY
- Add overClauseToJSON function for proper marshalling
- Enable 4 WithinGroupTests (130, 140, both baseline and regular)

Author: claude

ast/function_call.go

@@ -28,7 +28,8 @@ func (*UserDefinedTypeCallTarget) callTarget() {}
 
 // OverClause represents an OVER clause for window functions.
 type OverClause struct {
-	// Add partition by, order by, and window frame as needed
+	Partitions    []ScalarExpression `json:"Partitions,omitempty"`
+	OrderByClause *OrderByClause     `json:"OrderByClause,omitempty"`
 }
 
 // WithinGroupClause represents a WITHIN GROUP clause for ordered set aggregate functions.

parser/marshal.go

@@ -1389,9 +1389,7 @@ func scalarExpressionToJSON(expr ast.ScalarExpression) jsonNode {
 			node["WithinGroupClause"] = withinGroupClauseToJSON(e.WithinGroupClause)
 		}
 		if e.OverClause != nil {
-			node["OverClause"] = jsonNode{
-				"$type": "OverClause",
-			}
+			node["OverClause"] = overClauseToJSON(e.OverClause)
 		}
 		if len(e.IgnoreRespectNulls) > 0 {
 			idents := make([]jsonNode, len(e.IgnoreRespectNulls))
@@ -2151,6 +2149,23 @@ func withinGroupClauseToJSON(wg *ast.WithinGroupClause) jsonNode {
 	return node
 }
 
+func overClauseToJSON(oc *ast.OverClause) jsonNode {
+	node := jsonNode{
+		"$type": "OverClause",
+	}
+	if len(oc.Partitions) > 0 {
+		partitions := make([]jsonNode, len(oc.Partitions))
+		for i, p := range oc.Partitions {
+			partitions[i] = scalarExpressionToJSON(p)
+		}
+		node["Partitions"] = partitions
+	}
+	if oc.OrderByClause != nil {
+		node["OrderByClause"] = orderByClauseToJSON(oc.OrderByClause)
+	}
+	return node
+}
+
 // ======================= New Statement JSON Functions =======================
 
 func tableHintToJSON(h ast.TableHintType) jsonNode {

parser/parse_select.go

@@ -1374,14 +1374,44 @@ func (p *Parser) parsePostExpressionAccess(expr ast.ScalarExpression) (ast.Scala
 			}
 			p.nextToken() // consume (
 
-			// For now, just skip to closing paren (basic OVER() support)
-			// TODO: Parse partition by, order by, and window frame
+			overClause := &ast.OverClause{}
+
+			// Parse PARTITION BY
+			if strings.ToUpper(p.curTok.Literal) == "PARTITION" {
+				p.nextToken() // consume PARTITION
+				if strings.ToUpper(p.curTok.Literal) == "BY" {
+					p.nextToken() // consume BY
+				}
+				// Parse partition expressions
+				for p.curTok.Type != TokenRParen && p.curTok.Type != TokenEOF {
+					partExpr, err := p.parseScalarExpression()
+					if err != nil {
+						return nil, err
+					}
+					overClause.Partitions = append(overClause.Partitions, partExpr)
+					if p.curTok.Type == TokenComma {
+						p.nextToken()
+					} else {
+						break
+					}
+				}
+			}
+
+			// Parse ORDER BY
+			if p.curTok.Type == TokenOrder {
+				orderBy, err := p.parseOrderByClause()
+				if err != nil {
+					return nil, err
+				}
+				overClause.OrderByClause = orderBy
+			}
+
 			if p.curTok.Type != TokenRParen {
 				return nil, fmt.Errorf("expected ) in OVER clause, got %s", p.curTok.Literal)
 			}
 			p.nextToken() // consume )
 
-			fc.OverClause = &ast.OverClause{}
+			fc.OverClause = overClause
 		}
 
 		break

parser/testdata/Baselines130_WithinGroupTests130/metadata.json

@@ -1 +1 @@
-{"todo": true}
+{}

parser/testdata/Baselines140_WithinGroupTests140/metadata.json

@@ -1 +1 @@
-{"todo": true}
+{}

parser/testdata/WithinGroupTests130/metadata.json

@@ -1 +1 @@
-{"todo": true}
+{}

parser/testdata/WithinGroupTests140/metadata.json

@@ -1 +1 @@
-{"todo": true}
+{}