string strSQL="select members.unitname as postunitname from bbs,members where bbs.postuser=members.userid";
string strSQL1="select members.unitname as replyunitname from bbs,members where bbs.replyuser=members.userid";问题:
请问以上两个SQL语句能不能合并成一个,合并后执行的效率会不会更好?谢谢!
string strSQL1="select members.unitname as replyunitname from bbs,members where bbs.replyuser=members.userid";问题:
请问以上两个SQL语句能不能合并成一个,合并后执行的效率会不会更好?谢谢!
解决方案 »
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----------------
那我所需要的replyunitname呢?
union
select members.unitname as replyunitname from bbs,members where bbs.replyuser=members.userid
FROM BBS
LEFT JOIN Members M1 ON M1.UserID=BBS.PostUser
LEFT JOIN Members M2 ON M2.UserID=BBS.ReplyUser
union
select members.unitname,'replyunitname' as type from bbs,members where bbs.replyuser=members.userid
create proc proc_system_user_Filter
(
@userid varchar(20);
)
as
select members.unitname as postunitname from bbs,members where bbs.postuser=@useridselect members.unitname as replyunitname from bbs,members where bbs.replyuser=@userid
SELECT dbo.TB_ORDERS.OrderID, dbo.TB_ORDERS.OrderDate,
dbo.TB_ORDERS.OrderState, dbo.TB_ORDERS.UserCode,
dbo.TB_System_Power.PowerName, dbo.TB_ORDERS.ReplaceUserCode
FROM dbo.TB_ORDERS INNER JOIN
dbo.TB_System_Power ON
dbo.TB_ORDERS.UserCode = dbo.TB_System_Power.UserCode LEFT OUTER JOIN
dbo.TB_System_Power TB_System_Power_1 ON
FROM BBS
LEFT JOIN Members M1 ON M1.UserID=BBS.PostUser
LEFT JOIN Members M2 ON M2.UserID=BBS.ReplyUser
-----------------------------------
不行,出错
LEFT JOIN Members M2 ON M2.UserID=BBS.ReplyUser
说这两句有语法错误,对了,是不是我的数据库是ACCESS
LEFT JOIN Members M2 ON M2.UserID=BBS.ReplyUser
FROM BBS,members as m1,members as m2 where bbs.postuser=m1.userid and bbs.replyuser=m2.userid我自己这样写了个SQL语句不知道有问题没
http://community.csdn.net/Expert/topic/4506/4506432.xml?temp=.6742365
SELECT d.UnitName AS PostUnitName,M2.UnitName AS ReplyUnitName
FROM (
SELECT BBS.PostUser,BBS.ReplyUser,M1.UnitName
FROM BBS LEFT JOIN Members M1 ON M1.UserID=BBS.PostUser)
d
LEFT JOIN Members M2 ON M2.UserID=d.ReplyUser