update bd_billtype a set a.forwardbilltype = case when a.forwardbilltype is null then 'YHHD' else a.forwardbilltype || ',YHHD' end where a.parentbilltype in ('F2','F3','F4','F5') or a.pk_billtypecode in ('F2','F3','F4','F5','36K4','36K6','36S4','36C9','36J5','36J7');上面这个语句执行报错,不识别 || 符号,请帮忙看看