sql优化记录

1.两个表通过多条件连接时有两种写法：

1）select bi.ZCID,re.ROLLZCID
from dicp2.dbo.BluePrintInfo bi join RollEntity re
on (bi.RefRollID=re.RollID or (bi.ProjectPhaseCode=re.ProjectPhaseCode and bi.RollCode=re.RollCode))

2）select bi.ZCID,re.ROLLZCID
from dicp2.dbo.BluePrintInfo bi join RollEntity re
on (bi.RefRollID=re.RollID)
UNION
select bi.ZCID,re.ROLLZCID
from dicp2.dbo.BluePrintInfo bi join RollEntity re
 ON (bi.ProjectPhaseCode=re.ProjectPhaseCode and bi.RollCode=re.RollCode)

第二种写法比第一种写法速度快了几十倍。