Add PARALLEL WITH statement chaining and fix EXISTS TABLE explain format

- Add PARALLEL token to lexer keywords
- Add ParallelWithQuery AST node for chaining statements with PARALLEL WITH
- Add parseParallelWith in parser to handle statement chaining
- Fix table expression alias handling to not consume PARALLEL when followed by WITH
- Fix ExistsTableQuery explain output to match ClickHouse format (space alignment for missing database)

Tests fixed:
- 03305_parallel_with (all statements)
- 03604_parallel_with_query_lock (all statements)
- 01048_exists_query (all statements)
- 00101_materialized_views_and_insert_without_explicit_database (exists-related)
- 01073_attach_if_not_exists

Author: claude

ast/ast.go

@@ -1597,3 +1597,13 @@ type ExistsExpr struct {
 func (e *ExistsExpr) Pos() token.Position { return e.Position }
 func (e *ExistsExpr) End() token.Position { return e.Position }
 func (e *ExistsExpr) expressionNode()     {}
+
+// ParallelWithQuery represents multiple statements executed in parallel with PARALLEL WITH.
+type ParallelWithQuery struct {
+	Position   token.Position `json:"-"`
+	Statements []Statement    `json:"statements"`
+}
+
+func (p *ParallelWithQuery) Pos() token.Position { return p.Position }
+func (p *ParallelWithQuery) End() token.Position { return p.Position }
+func (p *ParallelWithQuery) statementNode()      {}

internal/explain/explain.go

@@ -246,6 +246,8 @@ func Node(sb *strings.Builder, node interface{}, depth int) {
 		explainCreateIndexQuery(sb, n, indent, depth)
 	case *ast.UpdateQuery:
 		explainUpdateQuery(sb, n, indent, depth)
+	case *ast.ParallelWithQuery:
+		explainParallelWithQuery(sb, n, indent, depth)
 
 	// Types
 	case *ast.DataType:

internal/explain/statements.go

@@ -1006,7 +1006,7 @@ func explainExistsTableQuery(sb *strings.Builder, n *ast.ExistsQuery, indent str
 	}
 
 	// For TABLE/DICTIONARY/VIEW, show database and object name
-	name := n.Table
+	name := " " + n.Table // Prefix with space for alignment (where database would be)
 	children := 1
 	if n.Database != "" {
 		name = n.Database + " " + n.Table
@@ -1690,3 +1690,39 @@ func explainUpdateQuery(sb *strings.Builder, n *ast.UpdateQuery, indent string,
 		Node(sb, assign, depth+2)
 	}
 }
+
+func explainParallelWithQuery(sb *strings.Builder, n *ast.ParallelWithQuery, indent string, depth int) {
+	if n == nil || len(n.Statements) == 0 {
+		fmt.Fprintf(sb, "%sParallelWithQuery\n", indent)
+		return
+	}
+
+	// Build the name from the first statement
+	name := getParallelWithName(n.Statements[0])
+	count := len(n.Statements)
+
+	fmt.Fprintf(sb, "%sParallelWithQuery %d %s (children %d)\n", indent, count, name, count)
+
+	for _, stmt := range n.Statements {
+		Node(sb, stmt, depth+1)
+	}
+}
+
+func getParallelWithName(stmt ast.Statement) string {
+	switch s := stmt.(type) {
+	case *ast.DropQuery:
+		tableName := ""
+		if len(s.Tables) > 0 {
+			if s.Tables[0].Table != "" {
+				tableName = s.Tables[0].Table
+			}
+		}
+		return "DropQuery__" + tableName
+	case *ast.CreateQuery:
+		return "CreateQuery_" + s.Table
+	case *ast.InsertQuery:
+		return "InsertQuery__"
+	default:
+		return "Statement"
+	}
+}

parser/expression.go

@@ -272,6 +272,10 @@ func (p *Parser) parseImplicitAlias(expr ast.Expression) ast.Expression {
 		if upper == "INTERSECT" {
 			return expr
 		}
+		// Don't consume PARALLEL as alias if followed by WITH (parallel query syntax)
+		if p.currentIs(token.PARALLEL) && p.peekIs(token.WITH) {
+			return expr
+		}
 		// Don't consume window frame keywords as implicit aliases
 		switch upper {
 		case "ROWS", "RANGE", "GROUPS", "UNBOUNDED", "PRECEDING", "FOLLOWING", "CURRENT":

parser/parser.go

@@ -99,6 +99,10 @@ func (p *Parser) ParseStatements(ctx context.Context) ([]ast.Statement, error) {
 
 		stmt := p.parseStatement()
 		if stmt != nil {
+			// Check for PARALLEL WITH to chain statements
+			if p.currentIs(token.PARALLEL) && p.peekIs(token.WITH) {
+				stmt = p.parseParallelWith(stmt)
+			}
 			statements = append(statements, stmt)
 		}
 
@@ -114,6 +118,25 @@ func (p *Parser) ParseStatements(ctx context.Context) ([]ast.Statement, error) {
 	return statements, nil
 }
 
+// parseParallelWith parses PARALLEL WITH clauses to chain statements
+func (p *Parser) parseParallelWith(first ast.Statement) *ast.ParallelWithQuery {
+	parallel := &ast.ParallelWithQuery{
+		Position:   first.Pos(),
+		Statements: []ast.Statement{first},
+	}
+
+	for p.currentIs(token.PARALLEL) && p.peekIs(token.WITH) {
+		p.nextToken() // skip PARALLEL
+		p.nextToken() // skip WITH
+		stmt := p.parseStatement()
+		if stmt != nil {
+			parallel.Statements = append(parallel.Statements, stmt)
+		}
+	}
+
+	return parallel
+}
+
 func (p *Parser) parseStatement() ast.Statement {
 	switch p.current.Token {
 	case token.SELECT:
@@ -1343,6 +1366,10 @@ func (p *Parser) parseTableExpression() *ast.TableExpression {
 			p.nextToken()
 		}
 	} else if (p.currentIs(token.IDENT) || p.current.Token.IsKeyword()) && !p.isKeywordForClause() {
+		// Don't consume PARALLEL as alias if followed by WITH (parallel query syntax)
+		if p.currentIs(token.PARALLEL) && p.peekIs(token.WITH) {
+			return expr
+		}
 		expr.Alias = p.current.Value
 		p.nextToken()
 	}

parser/testdata/00101_materialized_views_and_insert_without_explicit_database/metadata.json

@@ -1,8 +1 @@
-{
-  "explain_todo": {
-    "stmt35": true,
-    "stmt36": true,
-    "stmt37": true,
-    "stmt38": true
-  }
-}
+{}

parser/testdata/01048_exists_query/metadata.json

@@ -1,7 +1 @@
-{
-  "explain_todo": {
-    "stmt22": true,
-    "stmt23": true,
-    "stmt24": true
-  }
-}
+{}

parser/testdata/01073_attach_if_not_exists/metadata.json

@@ -1,7 +1,6 @@
 {
   "explain_todo": {
     "stmt3": true,
-    "stmt5": true,
-    "stmt6": true
+    "stmt5": true
   }
 }

parser/testdata/03305_parallel_with/metadata.json

@@ -1,11 +1 @@
-{
-  "explain_todo": {
-    "stmt1": true,
-    "stmt2": true,
-    "stmt5": true,
-    "stmt6": true,
-    "stmt11": true,
-    "stmt13": true,
-    "stmt14": true
-  }
-}
+{}

parser/testdata/03604_parallel_with_query_lock/metadata.json

@@ -1,5 +1 @@
-{
-  "explain_todo": {
-    "stmt4": true
-  }
-}
+{}