Add implicit alias handling for EXTRACT and function arguments

Three changes to support implicit aliases (identifiers without AS):

1. Parser: Add parseImplicitAlias call after parsing EXTRACT FROM expr
   Fixes `EXTRACT(DAY FROM toDate(...) arg_1)` syntax

2. Parser: Add parseImplicitAlias calls in parseFunctionArgumentList
   Fixes implicit aliases on function arguments like `func('a' arg_1)`

3. Parser: Add parseImplicitAlias calls for regex-style extract function

4. Explain: Update handleDateDiff to support 4 arguments (with timezone)

Fixes 12 statements in test 02267_special_operator_parse_alias_check.

Author: claude

internal/explain/functions.go

@@ -372,9 +372,9 @@ func explainDateAddSubWithInterval(sb *strings.Builder, opFunc string, arg1, arg
 }
 
 // handleDateDiff handles DATE_DIFF/DATEDIFF
-// DATE_DIFF(unit, date1, date2) -> dateDiff('unit', date1, date2)
+// DATE_DIFF(unit, date1, date2[, timezone]) -> dateDiff('unit', date1, date2[, timezone])
 func handleDateDiff(sb *strings.Builder, n *ast.FunctionCall, alias string, indent string, depth int) bool {
-	if len(n.Arguments) != 3 {
+	if len(n.Arguments) < 3 || len(n.Arguments) > 4 {
 		return false
 	}
 
@@ -392,12 +392,17 @@ func handleDateDiff(sb *strings.Builder, n *ast.FunctionCall, alias string, inde
 		return false
 	}
 
+	argCount := 3
+	if len(n.Arguments) == 4 {
+		argCount = 4
+	}
+
 	if alias != "" {
 		fmt.Fprintf(sb, "%sFunction dateDiff (alias %s) (children %d)\n", indent, alias, 1)
 	} else {
 		fmt.Fprintf(sb, "%sFunction dateDiff (children %d)\n", indent, 1)
 	}
-	fmt.Fprintf(sb, "%s ExpressionList (children %d)\n", indent, 3)
+	fmt.Fprintf(sb, "%s ExpressionList (children %d)\n", indent, argCount)
 
 	// First arg: unit as lowercase string literal
 	fmt.Fprintf(sb, "%s  Literal \\'%s\\'\n", indent, strings.ToLower(unitName))
@@ -406,6 +411,11 @@ func handleDateDiff(sb *strings.Builder, n *ast.FunctionCall, alias string, inde
 	Node(sb, date1Arg, depth+2)
 	Node(sb, date2Arg, depth+2)
 
+	// Fourth arg: optional timezone
+	if len(n.Arguments) == 4 {
+		Node(sb, n.Arguments[3], depth+2)
+	}
+
 	return true
 }
 
@@ -1334,13 +1344,10 @@ func explainExtractExprWithAlias(sb *strings.Builder, n *ast.ExtractExpr, alias
 	// EXTRACT is represented as Function toYear, toMonth, etc.
 	// ClickHouse uses specific function names for date/time extraction
 	fnName := extractFieldToFunction(n.Field)
-	// Use alias from parameter, or fall back to expression's alias
-	effectiveAlias := alias
-	if effectiveAlias == "" {
-		effectiveAlias = n.Alias
-	}
-	if effectiveAlias != "" {
-		fmt.Fprintf(sb, "%sFunction %s (alias %s) (children %d)\n", indent, fnName, effectiveAlias, 1)
+	// Only use the external alias parameter (from explicit AS on EXTRACT itself)
+	// NOT the alias from the From expression - that stays on the inner expression
+	if alias != "" {
+		fmt.Fprintf(sb, "%sFunction %s (alias %s) (children %d)\n", indent, fnName, alias, 1)
 	} else {
 		fmt.Fprintf(sb, "%sFunction %s (children %d)\n", indent, fnName, 1)
 	}

parser/expression.go

@@ -143,6 +143,8 @@ func (p *Parser) parseFunctionArgumentList() []ast.Expression {
 
 	expr := p.parseExpression(LOWEST)
 	if expr != nil {
+		// Handle implicit alias (identifier without AS)
+		expr = p.parseImplicitAlias(expr)
 		exprs = append(exprs, expr)
 	}
 
@@ -154,6 +156,8 @@ func (p *Parser) parseFunctionArgumentList() []ast.Expression {
 		}
 		expr := p.parseExpression(LOWEST)
 		if expr != nil {
+			// Handle implicit alias (identifier without AS)
+			expr = p.parseImplicitAlias(expr)
 			exprs = append(exprs, expr)
 		}
 	}
@@ -1390,6 +1394,8 @@ func (p *Parser) parseExtract() ast.Expression {
 			if p.currentIs(token.FROM) {
 				p.nextToken()
 				from := p.parseExpression(LOWEST)
+				// Handle implicit alias (identifier without AS)
+				from = p.parseImplicitAlias(from)
 				p.expect(token.RPAREN)
 				return &ast.ExtractExpr{
 					Position: pos,
@@ -1425,7 +1431,10 @@ func (p *Parser) parseExtract() ast.Expression {
 	// or extract(expr, pattern) where expr can be any expression
 	var args []ast.Expression
 	for !p.currentIs(token.RPAREN) && !p.currentIs(token.EOF) {
-		args = append(args, p.parseExpression(LOWEST))
+		arg := p.parseExpression(LOWEST)
+		// Handle implicit alias (identifier without AS)
+		arg = p.parseImplicitAlias(arg)
+		args = append(args, arg)
 		if p.currentIs(token.COMMA) {
 			p.nextToken()
 		} else {

parser/testdata/02267_special_operator_parse_alias_check/metadata.json

@@ -1,16 +1 @@
-{
-  "explain_todo": {
-    "stmt41": true,
-    "stmt43": true,
-    "stmt46": true,
-    "stmt48": true,
-    "stmt50": true,
-    "stmt52": true,
-    "stmt54": true,
-    "stmt56": true,
-    "stmt57": true,
-    "stmt58": true,
-    "stmt60": true,
-    "stmt62": true
-  }
-}
+{}