如果我这样说:
SELECT TOP(10000) ProductId from ProductInfo WHERE ProductId IN
(
SELECT ProductId from DeletedProduct
)
它是否能够在整张桌子上扫描,或一旦发现10 000头就消失?
它一旦发现10 000个,就将停止。
你们是否没有利用我的DELETE解决办法?
我认为,如果你加入进来,你的询问就会更快:
SELECT TOP(10000) P.ProductId
FROM ProductInfo P INNER JOIN DeletedProduct D on P.ProductId=D.ProductId
如果你只是对产品信息数据库(而不是其他栏目)感兴趣,并且只是为了核实产品实际存在,那么这种产品可能更快。
在管理室里,把你的询问和下面的问询合并在一起,表明贵方的费用为99%,而以下成本为1%(越快);但是,这只能归功于我正在使用的数据库。
SELECT TOP(10000) ProductId
FROM DeletedProduct D
WHERE EXISTS (SELECT * FROM ProductInfo P WHERE P.ProductID=D.ProductID )
For MSSQL, it will definitely index or table scan DeletedProduct since you are selecting all records there. At a guess, it will probably also do a index scan on ProductInfo unless there are >>> more than 10 000 records in it, and also unless the clustered index is on ProductId (but y, it will only read the pages needed to fill 10 000 records)
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