Add TRUNCATE DATABASE support

Parse TRUNCATE DATABASE differently from TRUNCATE TABLE and format
with the correct spacing in EXPLAIN output. ClickHouse uses different
spacing conventions for these two variants.

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

Author: kyleconroy

ast/ast.go

@@ -711,13 +711,14 @@ const (
 
 // TruncateQuery represents a TRUNCATE statement.
 type TruncateQuery struct {
-	Position  token.Position `json:"-"`
-	Temporary bool           `json:"temporary,omitempty"`
-	IfExists  bool           `json:"if_exists,omitempty"`
-	Database  string         `json:"database,omitempty"`
-	Table     string         `json:"table"`
-	OnCluster string         `json:"on_cluster,omitempty"`
-	Settings  []*SettingExpr `json:"settings,omitempty"`
+	Position         token.Position `json:"-"`
+	Temporary        bool           `json:"temporary,omitempty"`
+	IfExists         bool           `json:"if_exists,omitempty"`
+	TruncateDatabase bool           `json:"truncate_database,omitempty"` // True for TRUNCATE DATABASE
+	Database         string         `json:"database,omitempty"`
+	Table            string         `json:"table"`
+	OnCluster        string         `json:"on_cluster,omitempty"`
+	Settings         []*SettingExpr `json:"settings,omitempty"`
 }
 
 func (t *TruncateQuery) Pos() token.Position { return t.Position }

internal/explain/statements.go

@@ -2332,7 +2332,12 @@ func explainTruncateQuery(sb *strings.Builder, n *ast.TruncateQuery, indent stri
 		if hasSettings {
 			children++
 		}
-		fmt.Fprintf(sb, "%sTruncateQuery  %s (children %d)\n", indent, n.Table, children)
+		// TRUNCATE DATABASE has different spacing than TRUNCATE TABLE
+		if n.TruncateDatabase {
+			fmt.Fprintf(sb, "%sTruncateQuery %s  (children %d)\n", indent, n.Table, children)
+		} else {
+			fmt.Fprintf(sb, "%sTruncateQuery  %s (children %d)\n", indent, n.Table, children)
+		}
 		fmt.Fprintf(sb, "%s Identifier %s\n", indent, n.Table)
 	}
 	if hasSettings {

parser/parser.go

@@ -6147,8 +6147,12 @@ func (p *Parser) parseTruncate() *ast.TruncateQuery {
 		p.nextToken()
 	}
 
+	// Handle TABLE or DATABASE keyword
 	if p.currentIs(token.TABLE) {
 		p.nextToken()
+	} else if p.currentIs(token.DATABASE) {
+		trunc.TruncateDatabase = true
+		p.nextToken()
 	}
 
 	// Handle IF EXISTS

parser/testdata/02842_truncate_database/metadata.json

@@ -1,5 +1 @@
-{
-  "explain_todo": {
-    "stmt33": true
-  }
-}
+{}