Add INTERSECT keyword and fix EXCEPT explain formatting

- Add INTERSECT as a proper keyword token (was being parsed as identifier
  which caused it to be treated as an alias for function calls)
- Update parser to use token.INTERSECT instead of identifier check
- Fix explainSelectIntersectExceptQuery to wrap first operand in
  SelectWithUnionQuery when EXCEPT is present (matches ClickHouse behavior)
- Update metadata.json files to reflect newly passing explain tests

This fixes 12 INTERSECT/EXCEPT explain tests. Remaining failures require
parser changes to handle INTERSECT/EXCEPT operator precedence properly.

Author: claude

internal/explain/select.go

@@ -9,8 +9,26 @@ import (
 
 func explainSelectIntersectExceptQuery(sb *strings.Builder, n *ast.SelectIntersectExceptQuery, indent string, depth int) {
 	fmt.Fprintf(sb, "%sSelectIntersectExceptQuery (children %d)\n", indent, len(n.Selects))
-	for _, sel := range n.Selects {
-		Node(sb, sel, depth+1)
+
+	// ClickHouse wraps first operand in SelectWithUnionQuery when EXCEPT is present
+	hasExcept := false
+	for _, op := range n.Operators {
+		if op == "EXCEPT" {
+			hasExcept = true
+			break
+		}
+	}
+
+	childIndent := strings.Repeat(" ", depth+1)
+	for i, sel := range n.Selects {
+		if hasExcept && i == 0 {
+			// Wrap first operand in SelectWithUnionQuery -> ExpressionList format
+			fmt.Fprintf(sb, "%sSelectWithUnionQuery (children 1)\n", childIndent)
+			fmt.Fprintf(sb, "%s ExpressionList (children 1)\n", childIndent)
+			Node(sb, sel, depth+3)
+		} else {
+			Node(sb, sel, depth+1)
+		}
 	}
 }
 

parser/parser.go

@@ -314,8 +314,7 @@ func (p *Parser) parseSelectWithUnion() *ast.SelectWithUnionQuery {
 	}
 
 	// Parse UNION/INTERSECT ALL/EXCEPT ALL clauses
-	for p.currentIs(token.UNION) || p.currentIs(token.EXCEPT) ||
-		(p.currentIs(token.IDENT) && strings.ToUpper(p.current.Value) == "INTERSECT") {
+	for p.currentIs(token.UNION) || p.currentIs(token.EXCEPT) || p.currentIs(token.INTERSECT) {
 		var setOp string
 		if p.currentIs(token.UNION) {
 			setOp = "UNION"
@@ -366,8 +365,7 @@ func (p *Parser) parseSelectWithUnion() *ast.SelectWithUnionQuery {
 // Only INTERSECT ALL and EXCEPT ALL are flattened (no wrapper).
 // INTERSECT DISTINCT, INTERSECT, EXCEPT DISTINCT, and EXCEPT all use the wrapper.
 func (p *Parser) isIntersectExceptWithWrapper() bool {
-	if !p.currentIs(token.EXCEPT) &&
-		!(p.currentIs(token.IDENT) && strings.ToUpper(p.current.Value) == "INTERSECT") {
+	if !p.currentIs(token.EXCEPT) && !p.currentIs(token.INTERSECT) {
 		return false
 	}
 	// INTERSECT ALL and EXCEPT ALL are flattened (no wrapper)

parser/testdata/00174_distinct_in_order/metadata.json

@@ -1 +1 @@
-{"explain_todo":{"stmt17":true,"stmt9":true}}
+{}

parser/testdata/02004_intersect_except_const_column/metadata.json

@@ -1,17 +1,8 @@
 {
   "explain_todo": {
-    "stmt10": true,
-    "stmt11": true,
     "stmt12": true,
     "stmt13": true,
     "stmt14": true,
-    "stmt2": true,
-    "stmt3": true,
-    "stmt4": true,
-    "stmt5": true,
-    "stmt6": true,
-    "stmt7": true,
-    "stmt8": true,
-    "stmt9": true
+    "stmt2": true
   }
 }

parser/testdata/02004_intersect_except_distinct_operators/metadata.json

@@ -7,34 +7,22 @@
     "stmt14": true,
     "stmt15": true,
     "stmt16": true,
-    "stmt17": true,
     "stmt18": true,
-    "stmt20": true,
     "stmt21": true,
     "stmt22": true,
     "stmt23": true,
-    "stmt24": true,
-    "stmt25": true,
     "stmt26": true,
     "stmt27": true,
     "stmt28": true,
-    "stmt30": true,
     "stmt31": true,
     "stmt32": true,
     "stmt33": true,
     "stmt34": true,
     "stmt35": true,
     "stmt36": true,
-    "stmt37": true,
     "stmt38": true,
     "stmt39": true,
-    "stmt41": true,
     "stmt42": true,
-    "stmt45": true,
-    "stmt5": true,
-    "stmt6": true,
-    "stmt7": true,
-    "stmt8": true,
-    "stmt9": true
+    "stmt45": true
   }
 }

parser/testdata/02004_intersect_except_operators/metadata.json

@@ -5,35 +5,23 @@
     "stmt12": true,
     "stmt13": true,
     "stmt14": true,
-    "stmt15": true,
     "stmt16": true,
-    "stmt18": true,
     "stmt19": true,
     "stmt20": true,
     "stmt21": true,
-    "stmt22": true,
-    "stmt23": true,
     "stmt24": true,
     "stmt25": true,
     "stmt26": true,
-    "stmt28": true,
     "stmt29": true,
-    "stmt3": true,
     "stmt30": true,
     "stmt31": true,
     "stmt32": true,
     "stmt33": true,
     "stmt34": true,
-    "stmt35": true,
     "stmt36": true,
     "stmt37": true,
-    "stmt39": true,
-    "stmt4": true,
     "stmt40": true,
     "stmt43": true,
-    "stmt5": true,
-    "stmt6": true,
-    "stmt7": true,
     "stmt8": true,
     "stmt9": true
   }

parser/testdata/02044_exists_operator/metadata.json

@@ -1 +1 @@
-{"explain_todo":{"stmt2":true,"stmt5":true}}
+{}

parser/testdata/02317_distinct_in_order_optimization/metadata.json

@@ -1,7 +1 @@
-{
-  "explain_todo": {
-    "stmt60": true,
-    "stmt68": true,
-    "stmt76": true
-  }
-}
+{}

parser/testdata/02552_sparse_columns_intersect/metadata.json

@@ -1,7 +1,5 @@
 {
   "explain_todo": {
-    "stmt3": true,
-    "stmt6": true,
-    "stmt7": true
+    "stmt3": true
   }
 }

parser/testdata/03008_uniq_exact_equal_ranges/metadata.json

@@ -1,6 +1 @@
-{
-  "explain_todo": {
-    "stmt20": true,
-    "stmt21": true
-  }
-}
+{}