SelectWithUnionQuery (children 1)
 ExpressionList (children 1)
  SelectQuery (children 1)
   ExpressionList (children 1)
    Function equals (children 1)
     ExpressionList (children 2)
      Function concatWithSeparator (children 1)
       ExpressionList (children 3)
        Literal NULL
        Literal \'a\'
        Literal \'b\'
      Literal NULL
