Sybase SQL update with self-join

Question

Sybase SQL中使用自联接执行更新的正确语法是什么？例如，假设您有下表(#tmptbl)：

account | client  |amount | date
-------------------------------------
ACT1    | CLIENTA | 12    |2010-12-30
ACT2    | CLIENTB | 5     |2010-12-30
ACT1    | CLIENTA | 17    |2010-12-31
ACT2    | CLIENTB | 6     |2010-12-31

我想用2010-12-30的金额值覆盖2010-12-31的金额。

我想写这样的东西：

update old
set old.amount = new.amount
from #tmptbl old,  #tmptbl new
where 
/*filter old*/
old.account = 'ACT1' 
and old.date = '2010-12-30' 
and old.client = 'CLIENTA' 
/* self-join new and old*/
and old.account = new.account 
and old.client = new.client 
/* filter new */
and new.date = '2010-12-31' 

但看起来Sybase不接受“update<>”子句中的别名。这样做的正确方式是什么？

谢谢!

Answer 1

这是可行的：

update #tmptbl
set old.amount = new.amount
from #tmptbl old,  #tmptbl new
where 
/*filter old*/
old.account = 'ACT1' 
and old.date = '2010-12-30' 
and old.client = 'CLIENTA' 
/* self-join new and old*/
and old.account = new.account 
and old.client = new.client 
/* filter new */
and new.date = '2010-12-31' 
go

如果省略了要更新的表的别名，即set amount = new.amount，则Sybase会将正在更新的表与from子句中的第一个匹配表相关联，因此在这种情况下，要使更新起作用，您需要使用from读取from #tmptbl new, #tmptbl old。

输出：

 account     client     amount     date             
 ----------  ---------  ---------  ---------------- 
 ACT1        CLIENTA    12         30/12/2010 00:00 
 ACT2        CLIENTB    5          30/12/2010 00:00 
 ACT2        CLIENTB    6          31/12/2010 00:00 
 ACT1        CLIENTA    12         31/12/2010 00:00 

Answer 2

你试过了吗？

update #tmptbl 
set amount = new.amount
from #tmptbl old,  #tmptbl new
where 
/*filter old*/
old.account = 'ACT1' 
and old.date = '2010-12-30' 
and old.client = 'CLIENTA' 
/* self-join new and old*/
and old.account = new.account 
and old.client = new.client 
/* filter new */
and new.date = '2010-12-31'