Method parseTopClause

pkg/sql/parser/select.go:261–302

parseTopClause parses SQL Server's TOP n [PERCENT] [WITH TIES] clause. Returns nil when the current dialect is not SQL Server or TOP is absent. Note: "TOP" is detected via a string comparison rather than a dedicated token-type constant because the lexer does not define a TokenTypeTOP - it tokenises

()

// plain identifier/keyword literal.  A future lexer enhancement could introduce
// models.TokenTypeTop and replace the strings.ToUpper check below.
func (p *Parser) parseTopClause() (*ast.TopClause, error) {
	if p.dialect != string(keywords.DialectSQLServer) || strings.ToUpper(p.currentToken.Token.Value) != "TOP" {
		return nil, nil
	}
	p.advance() // Consume TOP

	hasParen := p.isType(models.TokenTypeLParen)
	if hasParen {
		p.advance() // Consume (
	}

	countExpr, err := p.parsePrimaryExpression()
	if err != nil {
		return nil, fmt.Errorf("expected expression after TOP: %w", err)
	}

	if hasParen {
		if !p.isType(models.TokenTypeRightParen) {
			return nil, p.expectedError(") after TOP expression")
		}
		p.advance() // Consume )
	}

	topClause := &ast.TopClause{Count: countExpr}

	// Optional PERCENT
	if p.isType(models.TokenTypePercent) ||
		(p.currentToken.Token.Type == models.TokenTypeKeyword && strings.ToUpper(p.currentToken.Token.Value) == "PERCENT") {
		topClause.IsPercent = true
		p.advance()
	}

	// Optional WITH TIES
	if p.isType(models.TokenTypeWith) && p.peekToken().Token.Type == models.TokenTypeTies {
		topClause.WithTies = true
		p.advance() // Consume WITH
		p.advance() // Consume TIES

	}

	return topClause, nil
}

// parseSelectColumnList parses the comma-separated column/expression list in SELECT.
func (p *Parser) parseSelectColumnList() ([]ast.Expression, error) {