Support CREATE INDEX expression without parentheses

ClickHouse allows CREATE INDEX without parentheses around the expression:
  CREATE INDEX idx ON tbl date(ts) TYPE MinMax

This commit:
- Parses unparenthesized expressions in CREATE INDEX
- Tracks whether columns were parenthesized for correct EXPLAIN output:
  - Single column in parens: Identifier
  - Multiple columns in parens: empty Function tuple
  - Unparenthesized expression: output directly

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: kyleconroy

ast/ast.go

@@ -1283,12 +1283,13 @@ func (d *DropWorkloadQuery) statementNode()      {}
 
 // CreateIndexQuery represents a CREATE INDEX statement.
 type CreateIndexQuery struct {
-	Position    token.Position `json:"-"`
-	IndexName   string         `json:"index_name"`
-	Table       string         `json:"table"`
-	Columns     []Expression   `json:"columns,omitempty"`
-	Type        string         `json:"type,omitempty"`        // Index type (minmax, bloom_filter, etc.)
-	Granularity int            `json:"granularity,omitempty"` // GRANULARITY value
+	Position             token.Position `json:"-"`
+	IndexName            string         `json:"index_name"`
+	Table                string         `json:"table"`
+	Columns              []Expression   `json:"columns,omitempty"`
+	ColumnsParenthesized bool           `json:"columns_parenthesized,omitempty"` // True if columns in (...)
+	Type                 string         `json:"type,omitempty"`                  // Index type (minmax, bloom_filter, etc.)
+	Granularity          int            `json:"granularity,omitempty"`           // GRANULARITY value
 }
 
 func (c *CreateIndexQuery) Pos() token.Position { return c.Position }

internal/explain/statements.go

@@ -2461,18 +2461,33 @@ func explainCreateIndexQuery(sb *strings.Builder, n *ast.CreateIndexQuery, inden
 	}
 	fmt.Fprintf(sb, "%s Index (children %d)\n", indent, indexChildren)
 
-	// For single column, output as Identifier
-	// For multiple columns or if there are any special cases, output as Function tuple
-	if len(n.Columns) == 1 {
-		if ident, ok := n.Columns[0].(*ast.Identifier); ok {
-			fmt.Fprintf(sb, "%s  Identifier %s\n", indent, ident.Name())
+	// Output columns based on whether they were parenthesized
+	if n.ColumnsParenthesized {
+		if len(n.Columns) == 1 {
+			// Single column in parentheses: output as identifier (if it's an identifier)
+			if ident, ok := n.Columns[0].(*ast.Identifier); ok {
+				fmt.Fprintf(sb, "%s  Identifier %s\n", indent, ident.Name())
+			} else {
+				// Non-identifier single expression - output directly
+				Node(sb, n.Columns[0], depth+2)
+			}
 		} else {
-			// Non-identifier expression - wrap in tuple
+			// Multiple columns in parentheses: output as empty Function tuple
 			fmt.Fprintf(sb, "%s  Function tuple (children 1)\n", indent)
 			fmt.Fprintf(sb, "%s   ExpressionList\n", indent)
 		}
+	} else if len(n.Columns) == 1 {
+		// Single unparenthesized expression: output directly
+		Node(sb, n.Columns[0], depth+2)
+	} else if len(n.Columns) > 0 {
+		// Multiple columns - wrap in Function tuple with ExpressionList
+		fmt.Fprintf(sb, "%s  Function tuple (children 1)\n", indent)
+		fmt.Fprintf(sb, "%s   ExpressionList (children %d)\n", indent, len(n.Columns))
+		for _, col := range n.Columns {
+			Node(sb, col, depth+3)
+		}
 	} else {
-		// Multiple columns or empty - always Function tuple with ExpressionList
+		// No columns - empty Function tuple
 		fmt.Fprintf(sb, "%s  Function tuple (children 1)\n", indent)
 		fmt.Fprintf(sb, "%s   ExpressionList\n", indent)
 	}

parser/parser.go

@@ -2352,8 +2352,9 @@ func (p *Parser) parseCreateIndex(pos token.Position) *ast.CreateIndexQuery {
 		query.Table = p.parseIdentifierName()
 	}
 
-	// Parse column list in parentheses
+	// Parse column expression - can be in parentheses or directly after table name
 	if p.currentIs(token.LPAREN) {
+		query.ColumnsParenthesized = true
 		p.nextToken() // skip (
 
 		for !p.currentIs(token.RPAREN) && !p.currentIs(token.EOF) {
@@ -2375,6 +2376,12 @@ func (p *Parser) parseCreateIndex(pos token.Position) *ast.CreateIndexQuery {
 		if p.currentIs(token.RPAREN) {
 			p.nextToken() // skip )
 		}
+	} else if !p.currentIs(token.SEMICOLON) && !p.currentIs(token.EOF) &&
+		!(p.currentIs(token.IDENT) && strings.ToUpper(p.current.Value) == "TYPE") {
+		// Expression directly after table name without parentheses
+		// e.g., CREATE INDEX idx ON tbl date(ts) TYPE MinMax
+		col := p.parseExpression(0)
+		query.Columns = append(query.Columns, col)
 	}
 
 	// Parse TYPE clause

parser/testdata/02487_create_index_normalize_functions/metadata.json

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