feat: implement TRUNCATE TABLE statement (SQL:2008)

pkg/models/token_type.go

@@ -277,6 +277,7 @@ const (
 	TokenTypeRefresh      TokenType = 375
 	TokenTypeTies         TokenType = 376 // TIES keyword for WITH TIES in FETCH clause
 	TokenTypePercent      TokenType = 377 // PERCENT keyword for FETCH ... PERCENT ROWS
+	TokenTypeTruncate     TokenType = 378 // TRUNCATE keyword for TRUNCATE TABLE statement
 
 	// Grouping Set Keywords (390-399)
 	TokenTypeGroupingSets TokenType = 390
@@ -545,6 +546,7 @@ var tokenStringMap = map[TokenType]string{
 	TokenTypeRefresh:      "REFRESH",
 	TokenTypeTies:         "TIES",
 	TokenTypePercent:      "PERCENT",
+	TokenTypeTruncate:     "TRUNCATE",
 
 	// Grouping Set Keywords
 	TokenTypeGroupingSets: "GROUPING_SETS",
@@ -666,7 +668,7 @@ func (t TokenType) IsDMLKeyword() bool {
 // IsDDLKeyword returns true if the token type is a DDL keyword
 func (t TokenType) IsDDLKeyword() bool {
 	switch t {
-	case TokenTypeCreate, TokenTypeAlter, TokenTypeDrop, TokenTypeTable,
+	case TokenTypeCreate, TokenTypeAlter, TokenTypeDrop, TokenTypeTruncate, TokenTypeTable,
 		TokenTypeIndex, TokenTypeView, TokenTypeColumn, TokenTypeDatabase,
 		TokenTypeSchema, TokenTypeTrigger:
 		return true

pkg/sql/ast/ast.go

@@ -1074,6 +1074,19 @@ func (d *DropStatement) statementNode()      {}
 func (d DropStatement) TokenLiteral() string { return "DROP " + d.ObjectType }
 func (d DropStatement) Children() []Node     { return nil }
 
+// TruncateStatement represents a TRUNCATE TABLE statement
+// Syntax: TRUNCATE [TABLE] table_name [, table_name ...] [RESTART IDENTITY | CONTINUE IDENTITY] [CASCADE | RESTRICT]
+type TruncateStatement struct {
+	Tables           []string // Table names to truncate
+	RestartIdentity  bool     // RESTART IDENTITY - reset sequences
+	ContinueIdentity bool     // CONTINUE IDENTITY - keep sequences (default)
+	CascadeType      string   // CASCADE, RESTRICT, or empty
+}
+
+func (t *TruncateStatement) statementNode()      {}
+func (t TruncateStatement) TokenLiteral() string { return "TRUNCATE TABLE" }
+func (t TruncateStatement) Children() []Node     { return nil }
+
 // PartitionDefinition represents a partition definition in CREATE TABLE
 // Syntax: PARTITION name VALUES { LESS THAN (expr) | IN (list) | FROM (expr) TO (expr) }
 type PartitionDefinition struct {

pkg/sql/keywords/keywords.go

@@ -156,6 +156,11 @@ var ADDITIONAL_KEYWORDS = []Keyword{
 	{Word: "OPTION", Type: models.TokenTypeKeyword, Reserved: false, ReservedForTableAlias: false},
 	{Word: "CASCADED", Type: models.TokenTypeKeyword, Reserved: false, ReservedForTableAlias: false},
 	{Word: "LOCAL", Type: models.TokenTypeKeyword, Reserved: false, ReservedForTableAlias: false},
+	// TRUNCATE TABLE statement (SQL:2008)
+	{Word: "TRUNCATE", Type: models.TokenTypeTruncate, Reserved: true, ReservedForTableAlias: true},
+	{Word: "RESTART", Type: models.TokenTypeKeyword, Reserved: false, ReservedForTableAlias: false},
+	{Word: "CONTINUE", Type: models.TokenTypeKeyword, Reserved: false, ReservedForTableAlias: false},
+	{Word: "IDENTITY", Type: models.TokenTypeKeyword, Reserved: false, ReservedForTableAlias: false},
 }
 
 // addKeywordsWithCategory is a helper method to add multiple keywords

pkg/sql/parser/ddl.go

@@ -804,3 +804,57 @@ func (p *Parser) parseRefreshStatement() (*ast.RefreshMaterializedViewStatement,
 
 	return stmt, nil
 }
+
+// parseTruncateStatement parses TRUNCATE TABLE statement
+// Syntax: TRUNCATE [TABLE] table_name [, table_name ...] [RESTART IDENTITY | CONTINUE IDENTITY] [CASCADE | RESTRICT]
+func (p *Parser) parseTruncateStatement() (*ast.TruncateStatement, error) {
+	stmt := &ast.TruncateStatement{}
+
+	// Optional TABLE keyword
+	if p.isType(models.TokenTypeTable) {
+		p.advance() // Consume TABLE
+	}
+
+	// Parse table names (can be comma-separated)
+	for {
+		if !p.isType(models.TokenTypeIdentifier) {
+			return nil, p.expectedError("table name")
+		}
+		stmt.Tables = append(stmt.Tables, p.currentToken.Literal)
+		p.advance()
+
+		if p.isType(models.TokenTypeComma) {
+			p.advance() // Consume comma
+			continue
+		}
+		break
+	}
+
+	// Parse optional RESTART IDENTITY / CONTINUE IDENTITY
+	if p.isTokenMatch("RESTART") {
+		p.advance() // Consume RESTART
+		if !p.isTokenMatch("IDENTITY") {
+			return nil, p.expectedError("IDENTITY after RESTART")
+		}
+		p.advance() // Consume IDENTITY
+		stmt.RestartIdentity = true
+	} else if p.isTokenMatch("CONTINUE") {
+		p.advance() // Consume CONTINUE
+		if !p.isTokenMatch("IDENTITY") {
+			return nil, p.expectedError("IDENTITY after CONTINUE")
+		}
+		p.advance() // Consume IDENTITY
+		stmt.ContinueIdentity = true
+	}
+
+	// Parse optional CASCADE/RESTRICT
+	if p.isType(models.TokenTypeCascade) {
+		stmt.CascadeType = "CASCADE"
+		p.advance()
+	} else if p.isType(models.TokenTypeRestrict) {
+		stmt.CascadeType = "RESTRICT"
+		p.advance()
+	}
+
+	return stmt, nil
+}

pkg/sql/parser/parser.go

@@ -222,7 +222,7 @@ func (p *Parser) Release() {
 }
 
 // parseStatement parses a single SQL statement
-// Uses fast int-based ModelType comparisons with fallback for hot path optimization
+// Uses O(1) switch dispatch on ModelType (compiles to jump table) for optimal performance
 func (p *Parser) parseStatement() (ast.Statement, error) {
 	// Check context if available
 	if p.ctx != nil {
@@ -264,6 +264,9 @@ func (p *Parser) parseStatement() (ast.Statement, error) {
 		case models.TokenTypeRefresh:
 			p.advance()
 			return p.parseRefreshStatement()
+		case models.TokenTypeTruncate:
+			p.advance()
+			return p.parseTruncateStatement()
 		}
 		// ModelType set but not a statement keyword - fall through to fallback
 	}
@@ -273,7 +276,6 @@ func (p *Parser) parseStatement() (ast.Statement, error) {
 	if p.isType(models.TokenTypeWith) {
 		return p.parseWithStatement()
 	}
-	// Use matchType() for check-and-advance pattern
 	if p.matchType(models.TokenTypeSelect) {
 		return p.parseSelectWithSetOperations()
 	}
@@ -301,6 +303,9 @@ func (p *Parser) parseStatement() (ast.Statement, error) {
 	if p.matchType(models.TokenTypeRefresh) {
 		return p.parseRefreshStatement()
 	}
+	if p.matchType(models.TokenTypeTruncate) {
+		return p.parseTruncateStatement()
+	}
 	return nil, p.expectedError("statement")
 }
 
@@ -387,6 +392,7 @@ var modelTypeToString = map[models.TokenType]token.Type{
 	models.TokenTypeCreate:       "CREATE",
 	models.TokenTypeAlter:        token.ALTER,
 	models.TokenTypeDrop:         token.DROP,
+	models.TokenTypeTruncate:     "TRUNCATE",
 	models.TokenTypeTable:        "TABLE",
 	models.TokenTypeIndex:        "INDEX",
 	models.TokenTypeView:         "VIEW",

pkg/sql/parser/token_converter.go

@@ -524,6 +524,7 @@ func buildTypeMapping() map[models.TokenType]token.Type {
 		models.TokenTypeCreate:   "CREATE",
 		models.TokenTypeAlter:    "ALTER",
 		models.TokenTypeDrop:     "DROP",
+		models.TokenTypeTruncate: "TRUNCATE",
 		models.TokenTypeTable:    "TABLE",
 		models.TokenTypeIndex:    "INDEX",
 		models.TokenTypeView:     "VIEW",