SelectWithUnionQuery (children 1)
 ExpressionList (children 1)
  SelectQuery (children 1)
   ExpressionList (children 2)
    Function isNull (children 1)
     ExpressionList (children 1)
      Function multiply (children 1)
       ExpressionList (children 2)
        Identifier a
        Identifier b
    Function isNotNull (children 1)
     ExpressionList (children 1)
      Function multiply (children 1)
       ExpressionList (children 2)
        Identifier a
        Identifier b