Method parseSelectColumnList

pkg/sql/parser/select.go:305–358

parseSelectColumnList parses the comma-separated column/expression list in SELECT.

()

// parseSelectColumnList parses the comma-separated column/expression list in SELECT.
func (p *Parser) parseSelectColumnList() ([]ast.Expression, error) {
	// Guard: SELECT immediately followed by FROM is an error.
	if p.isType(models.TokenTypeFrom) {
		return nil, goerrors.ExpectedTokenError(
			"column expression",
			"FROM",
			p.currentLocation(),
			"SELECT requires at least one column expression before FROM",
		)
	}

	columns := make([]ast.Expression, 0, 8)
	for {
		var expr ast.Expression

		if p.isType(models.TokenTypeAsterisk) || p.isType(models.TokenTypeMul) {
			// Both TokenTypeAsterisk and TokenTypeMul represent '*' in SQL.
			// The tokenizer may produce either depending on context.
			expr = &ast.Identifier{Name: "*"}
			p.advance()
		} else {
			var err error
			expr, err = p.parseExpression()
			if err != nil {
				return nil, err
			}

			// Optional alias: AS name  or  implicit name (non-identifier expressions only)
			if p.isType(models.TokenTypeAs) {
				p.advance() // Consume AS
				if !p.isIdentifier() {
					return nil, p.expectedError("alias name after AS")
				}
				alias := p.currentToken.Token.Value
				p.advance()
				expr = &ast.AliasedExpression{Expr: expr, Alias: alias}
			} else if p.canBeAlias() {
				if _, ok := expr.(*ast.Identifier); !ok {
					alias := p.currentToken.Token.Value
					p.advance()
					expr = &ast.AliasedExpression{Expr: expr, Alias: alias}
				}
			}
		}

		columns = append(columns, expr)

		if !p.isType(models.TokenTypeComma) {
			break
		}
		p.advance() // Consume comma
	}
	return columns, nil
}