假設遇到以下情形：（執行SQL更新語法）
update dbo.pre_case
set
pc_handle_ext=(select com_telext from common..comper cc
inner join common..orgcod co on cc.com_orgcd=co.org_orgcd
inner join common..depcod dp on cc.com_deptid=dp.dep_deptid
where com_empno=＠handleno),
pc_service_ext=(select com_telext from common..comper cc
inner join common..orgcod co on cc.com_orgcd=co.org_orgcd
inner join common..depcod dp on cc.com_deptid=dp.dep_deptid
where com_empno=＠handleno),
pc_service_dept=(select dep_deptname from common..comper cc
inner join common..orgcod co on cc.com_orgcd=co.org_orgcd
inner join common..depcod dp on cc.com_deptid=dp.dep_deptid
where com_empno=＠handleno)
where pc_no=＠id
發現有三部份相同的Select語法，
建議可改成：
declare ＠pc_handle_ext nvarchar(20);
declare ＠pc_service_ext nvarchar(20);
declare ＠pc_service_dept nvarchar(20);
select ＠pc_handle_ext=com_telext ,＠pc_service_ext=com_telext ,
＠pc_service_dept=dep_deptname
from common..comper cc
inner join common..orgcod co on cc.com_orgcd=co.org_orgcd
inner join common..depcod dp on cc.com_deptid=dp.dep_deptid
where com_empno=＠handleno
--先將要修改的值存於SQL變數中，不用跑三次，一次就解決
update dbo.pre_case
set
pc_handle_ext=＠pc_handle_ext,
pc_service_ext=＠pc_service_ext,
pc_service_dept=＠pc_service_dept
where pc_no=＠id
之後再執行一次SQL更新的語法，將＠變數值存入欄位裡即可
