SelectWithUnionQuery (children 1)
 ExpressionList (children 1)
  SelectQuery (children 1)
   ExpressionList (children 1)
    Function equals (children 1)
     ExpressionList (children 2)
      Function concat (children 1)
       ExpressionList (children 2)
        Literal \'a\'
        Function materialize (children 1)
         ExpressionList (children 1)
          Literal \'b\'
      Literal \'ab\'
