编程论坛 » SQL Server论坛 » 救助，关于union语句的优化

球球 发表于 2008-9-2 11:28

救助，关于union语句的优化

请问，下面的这条语句该怎么优化？
Select Count(*) as usercount from (

SELECT UserID FROM IPTV_COOK_PROGRESS where RowTime between '08-08-01' and '08-08-31'

UNION SELECT UserID FROM IPTV_FISH_HISTORY where RowTime between '08-08-01' and '08-08-31'

UNION SELECT UserID FROM IPTV_FIND_HISTORY where RowTime between '08-08-01' and '08-08-31'

UNION SELECT UserID FROM IPTV_QUIZ_HISTORY where RowTime between '08-08-01' and '08-08-31') a

bb3852 发表于 2008-9-2 13:13

1 * 改为1
2 union 改为union all
3 between and 改为>= <=
4 RowTime建立索引

球球 发表于 2008-9-5 02:09

谢谢。我分别在RowTime_UserID，RowTime，UserID上面创建了索引，查询百万条数据，从1万6毫秒提高到2百毫秒以内。

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