SelectWithUnionQuery (children 1)
 ExpressionList (children 1)
  SelectQuery (children 1)
   ExpressionList (children 1)
    Function sum (children 1)
     ExpressionList (children 1)
      Function in (children 1)
       ExpressionList (children 2)
        Function toNullable (children 1)
         ExpressionList (children 1)
          Literal \'a\'
        Literal \'a\'