select 语句的条件如何过滤的？

[yumanqing]

如下的SQL语句：

SELECT rdr.CusCode,
sum(case when rdr.cVouchType='430' AND  rdr.cWhCode ='001' AND rdr.iDate>='2008-01-01'  then rds.iQuantity else 0 end) as InQty,
sum(case when  rdr.cVouchType='430' AND  rdr.cWhCode ='001' AND rdr.iDate>='2008-01-01' then rds.Weight else 0 end) as  InWeight
FROM RdRecord rdr 
LEFT JOIN RdRecords rds ON  rdr.[ID]=rds.[ID] 
WHERE rdr.cWhCode ='001' AND rdr.iDate>='2008-01-01'
GROUP BY rdr.CusCode

WHERE 中的条件和Case中的条件过滤的先后顺序是怎么样的，我感觉不要WHERE语句也可以，而实际不行，原语句比这复杂的多，
且每个CASE中的条件不一样，如果WHERE 和 Case中的条件不一致究竟是怎么过滤的。谢谢！

[hyde100]

先where
符合where的再参与计算

[水族杰纶]

set showplan_text on
go
SELECT rdr.CusCode,
sum(case when rdr.cVouchType='430' AND  rdr.cWhCode ='001' AND rdr.iDate>='2008-01-01'  then rds.iQuantity else 0 end) as InQty,
sum(case when  rdr.cVouchType='430' AND  rdr.cWhCode ='001' AND rdr.iDate>='2008-01-01' then rds.Weight else 0 end) as  InWeight
FROM RdRecord rdr 
LEFT JOIN RdRecords rds ON  rdr.[ID]=rds.[ID] 
WHERE rdr.cWhCode ='001' AND rdr.iDate>='2008-01-01'
GROUP BY rdr.CusCode

[Yang_]

从性能角度
WHERE 部分宁可多余也不要不足

[csdyyr]

先过滤where,后过滤case

[ChinaJiaBing]

先执行的是，where->group by->case

[dawugui]

先where,然后再case.

不要where是不行的.

你的case中rdr.cWhCode ='001' AND rdr.iDate>='2008-01-01' 可以不要,直接放在where条件中即可.

[「已注销」]

--这个是用友的数据库,
--应该这样写
SELECT rdr.CusCode,
sum(ISNULL(rds.iQuantity,0)) as InQty,
sum(ISNULL(rds.Weight,0)) as  InWeight
FROM RdRecord rdr 
INNER JOIN RdRecords rds ON  rdr.[ID]=rds.[ID] AND rdr.cWhCode ='001' AND rdr.iDate>='2008-01-01' AND rdr.cVouchType='430' 
GROUP BY rdr.CusCode

[「已注销」]

既然你WHERE语句中已经指定了条件，就不要用CASE语句了，但是SUM的时候要把为空的语句给去掉，提高一下语句性能

[fcuandy]

从性能上海兄说过了。

从功能上来说，根本就不一样，
加了where和不加where产生的行数都不一定相等，又何来不加where 也可以呢 ？

[czx33859066]

加where 的SQL性能比没加的还是差别挺大的