Add support for SHOW and DESC/DESCRIBE statements (#180)

Co-authored-by: Copilot <[email protected]>
Co-authored-by: git-hulk <[email protected]>

Author: Copilot

parser/ast.go

@@ -8225,3 +8225,73 @@ func (g *GrantPrivilegeStmt) Accept(visitor ASTVisitor) error {
 	}
 	return visitor.VisitGrantPrivilegeExpr(g)
 }
+
+type ShowStmt struct {
+	ShowPos      Pos
+	StatementEnd Pos
+	ShowType     string           // e.g., "CREATE TABLE", "DATABASES", "TABLES"
+	Target       *TableIdentifier // for SHOW CREATE TABLE table_name
+}
+
+func (s *ShowStmt) Pos() Pos {
+	return s.ShowPos
+}
+
+func (s *ShowStmt) End() Pos {
+	if s.Target != nil {
+		return s.Target.End()
+	}
+	return s.StatementEnd
+}
+
+func (s *ShowStmt) String() string {
+	var builder strings.Builder
+	builder.WriteString("SHOW ")
+	builder.WriteString(s.ShowType)
+	if s.Target != nil {
+		builder.WriteString(" ")
+		builder.WriteString(s.Target.String())
+	}
+	return builder.String()
+}
+
+func (s *ShowStmt) Accept(visitor ASTVisitor) error {
+	visitor.Enter(s)
+	defer visitor.Leave(s)
+	if s.Target != nil {
+		if err := s.Target.Accept(visitor); err != nil {
+			return err
+		}
+	}
+	return visitor.VisitShowExpr(s)
+}
+
+type DescribeStmt struct {
+	DescribePos  Pos
+	StatementEnd Pos
+	Target       *TableIdentifier
+}
+
+func (d *DescribeStmt) Pos() Pos {
+	return d.DescribePos
+}
+
+func (d *DescribeStmt) End() Pos {
+	return d.Target.End()
+}
+
+func (d *DescribeStmt) String() string {
+	var builder strings.Builder
+	builder.WriteString("DESCRIBE ")
+	builder.WriteString(d.Target.String())
+	return builder.String()
+}
+
+func (d *DescribeStmt) Accept(visitor ASTVisitor) error {
+	visitor.Enter(d)
+	defer visitor.Leave(d)
+	if err := d.Target.Accept(visitor); err != nil {
+		return err
+	}
+	return visitor.VisitDescribeExpr(d)
+}

parser/ast_visitor.go

@@ -178,6 +178,8 @@ type ASTVisitor interface {
 	VisitExplainExpr(expr *ExplainStmt) error
 	VisitPrivilegeExpr(expr *PrivilegeClause) error
 	VisitGrantPrivilegeExpr(expr *GrantPrivilegeStmt) error
+	VisitShowExpr(expr *ShowStmt) error
+	VisitDescribeExpr(expr *DescribeStmt) error
 	VisitSelectItem(expr *SelectItem) error
 	VisitTargetPairExpr(expr *TargetPair) error
 
@@ -1430,6 +1432,20 @@ func (v *DefaultASTVisitor) VisitGrantPrivilegeExpr(expr *GrantPrivilegeStmt) er
 	return nil
 }
 
+func (v *DefaultASTVisitor) VisitShowExpr(expr *ShowStmt) error {
+	if v.Visit != nil {
+		return v.Visit(expr)
+	}
+	return nil
+}
+
+func (v *DefaultASTVisitor) VisitDescribeExpr(expr *DescribeStmt) error {
+	if v.Visit != nil {
+		return v.Visit(expr)
+	}
+	return nil
+}
+
 func (v *DefaultASTVisitor) VisitSelectItem(expr *SelectItem) error {
 	if v.Visit != nil {
 		return v.Visit(expr)

parser/parser_table.go

@@ -1116,6 +1116,10 @@ func (p *Parser) parseStmt(pos Pos) (Expr, error) {
 		expr, err = p.parseExplainStmt(pos)
 	case p.matchKeyword(KeywordGrant):
 		expr, err = p.parseGrantPrivilegeStmt(pos)
+	case p.matchKeyword(KeywordShow):
+		expr, err = p.parseShowStmt(pos)
+	case p.matchKeyword(KeywordDesc), p.matchKeyword(KeywordDescribe):
+		expr, err = p.parseDescribeStmt(pos)
 	default:
 		return nil, fmt.Errorf("unexpected token: %q", p.last().String)
 	}
@@ -1170,6 +1174,80 @@ func (p *Parser) parseUseStmt(pos Pos) (*UseStmt, error) {
 	}, nil
 }
 
+func (p *Parser) parseShowStmt(pos Pos) (*ShowStmt, error) {
+	if err := p.expectKeyword(KeywordShow); err != nil {
+		return nil, err
+	}
+
+	var showType string
+	var target *TableIdentifier
+
+	// Parse the type of SHOW statement
+	switch {
+	case p.matchKeyword(KeywordCreate):
+		// SHOW CREATE TABLE table_name
+		showType = "CREATE"
+		_ = p.lexer.consumeToken()
+
+		if err := p.expectKeyword(KeywordTable); err != nil {
+			return nil, err
+		}
+		showType += " TABLE"
+
+		tableIdent, err := p.parseTableIdentifier(p.Pos())
+		if err != nil {
+			return nil, err
+		}
+		target = tableIdent
+
+	case p.matchKeyword(KeywordDatabases):
+		// SHOW DATABASES
+		showType = "DATABASES"
+		_ = p.lexer.consumeToken()
+
+	case p.matchKeyword(KeywordTables):
+		// SHOW TABLES
+		showType = "TABLES"
+		_ = p.lexer.consumeToken()
+
+	default:
+		return nil, fmt.Errorf("expected CREATE, DATABASES, or TABLES after SHOW, got %q", p.last().String)
+	}
+
+	var statementEnd Pos
+	if target != nil {
+		statementEnd = target.End()
+	} else {
+		statementEnd = p.End()
+	}
+
+	return &ShowStmt{
+		ShowPos:      pos,
+		StatementEnd: statementEnd,
+		ShowType:     showType,
+		Target:       target,
+	}, nil
+}
+
+func (p *Parser) parseDescribeStmt(pos Pos) (*DescribeStmt, error) {
+	// DESC and DESCRIBE are both supported
+	if !p.matchKeyword(KeywordDesc) && !p.matchKeyword(KeywordDescribe) {
+		return nil, fmt.Errorf("expected DESC or DESCRIBE")
+	}
+	_ = p.lexer.consumeToken()
+
+	tableIdent, err := p.parseTableIdentifier(p.Pos())
+	if err != nil {
+		return nil, err
+	}
+
+	return &DescribeStmt{
+		DescribePos:  pos,
+		StatementEnd: tableIdent.End(),
+		Target:       tableIdent,
+	}, nil
+}
+
 // syntax: TRUNCATE TEMPORARY? TABLE (IF EXISTS)? tableIdentifier clusterClause?;
 func (p *Parser) parseTruncateTable(pos Pos) (*TruncateTable, error) {
 	if err := p.expectKeyword(KeywordTruncate); err != nil {

parser/testdata/ddl/desc_table.sql

@@ -0,0 +1 @@
+DESC mytable

parser/testdata/ddl/describe_table.sql

@@ -0,0 +1 @@
+DESCRIBE mytable

parser/testdata/ddl/format/desc_table.sql

@@ -0,0 +1,5 @@
+-- Origin SQL:
+DESC mytable
+
+-- Format SQL:
+DESCRIBE mytable;

parser/testdata/ddl/format/describe_table.sql

@@ -0,0 +1,5 @@
+-- Origin SQL:
+DESCRIBE mytable
+
+-- Format SQL:
+DESCRIBE mytable;

parser/testdata/ddl/format/show_create_table.sql

@@ -0,0 +1,5 @@
+-- Origin SQL:
+SHOW CREATE TABLE mytable
+
+-- Format SQL:
+SHOW CREATE TABLE mytable;

parser/testdata/ddl/format/show_databases.sql

@@ -0,0 +1,5 @@
+-- Origin SQL:
+SHOW DATABASES
+
+-- Format SQL:
+SHOW DATABASES;

parser/testdata/ddl/format/show_tables.sql

@@ -0,0 +1,5 @@
+-- Origin SQL:
+SHOW TABLES
+
+-- Format SQL:
+SHOW TABLES;