sql - 使用自联接更新 Sybase SQL

Question

Sybase SQL 中使用自连接进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 年 12 月 30 日的金额覆盖 2010 年 12 月 31 日的金额。

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 Sybase 似乎不接受“update <>”子句中的别名。这样做的正确方法是什么？

谢谢!

Answer 1

这有效:

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

如果您省略要更新的表的别名，即 set amount = new.amount，则 Sybase 会将您要更新的表与第一个匹配表关联起来在 from 子句中，因此在这种情况下，要使更新正常工作，您需要 from 来读取 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