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 toNullable (children 1)
       ExpressionList (children 1)
        Literal \'y\'
    Function toTypeName (children 1)
     ExpressionList (children 1)
      Identifier res
