SelectWithUnionQuery (children 1)
 ExpressionList (children 1)
  SelectQuery (children 1)
   ExpressionList (children 2)
    Function ifNull (alias res) (children 1)
     ExpressionList (children 2)
      Function materialize (children 1)
       ExpressionList (children 1)
        Literal \'x\'
      Function toNullable (children 1)
       ExpressionList (children 1)
        Literal \'y\'
    Function toTypeName (children 1)
     ExpressionList (children 1)
      Identifier res
