SelectWithUnionQuery (children 1)
 ExpressionList (children 1)
  SelectQuery (children 1)
   ExpressionList (children 1)
    Function has (children 1)
     ExpressionList (children 2)
      Literal Array_[\'a\', NULL, \'b\']
      Function materialize (children 1)
       ExpressionList (children 1)
        Literal \'c\'