在INNER JOIN之前如何执行WHERE子句 [英] How to do WHERE clause BEFORE INNER JOIN

问题描述

我该如何查询?

select Distinct  Station  , Slot , SubSlot, CompID , CompName 
from DeviceTrace as DT DT.DeviceID = '1339759958' 
inner join CompList as CL  
where  and DT.CompID = CL.CompID

我需要做DT.DeviceID = '1339759958'，然后再开始进行内部联接. 我使用sql server.

I need to do DT.DeviceID = '1339759958' before I start with the inner join. I work with sql server.

推荐答案

我很难相信它会带来任何改变.如果查询优化器计算出谓词效率更高，则应在连接之前应用谓词.唯一可能需要执行此操作的情况是，当优化程序做出错误选择时(至少对于内部联接而言-存在外部联接的有效情况).

I find it difficult to believe that it makes any difference. The query optimiser should apply the predicate before the join if it calculates that it is more efficient to do so. The only circumstance where you might need to do this is when the optimiser makes an erroneous choice (for inner joins at least -- there are valid cases for outer joins).

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