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