public function walkSelectExpression($selectExpression)
    {
        $expr = $selectExpression->expression;
        $sql  = parent::walkSelectExpression($selectExpression);

        if ($expr instanceof ReturnsGeometryInterface && !$selectExpression->hiddenAliasResultVariable) {
            $alias = trim(strrchr($sql, ' '));
            $this->rsm->typeMappings[$alias] = 'geometry';
        }

        return $sql;
    }