delete tblbillid where billid= (select * FROM tblbillid WHERE lastlogout < '2009-06-27')
改成
delete tblbillid a where EXISTS (select * FROM tblbillid WHERE lastlogout < '2009-06-27' AND billid=a.billid)
或
delete tblbillid where billid= (select billid FROM tblbillid WHERE lastlogout < '2009-06-27')
其他一样