union 組合

查詢單據，卻不知道單據在當前表還是在歷史表

select * from wms_bill where ... union select * from wms_billhistory  where ...

 

 

或者

 

if exists(select * from wms_bill where ..) begin select * from wms_bill where ...  end else begin select * from wms_billhistory  where ...