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SELECT a.TT_ID,A.TT_TAG,b.* FROM
(SELECT * FROM New_TopicTag WHERE TT_Tag='维修')as a
INNER JOIN New_Topic as b ON a.Tpc_ID = b.Tpc_ID
--2 sql
SELECT a.TT_ID,A.TT_TAG,b.* FROM New_TopicTag AS A
INNER JOIN New_Topic as b ON a.Tpc_ID = b.Tpc_ID
where a.TT_Tag='维修'
从执行计划上看无论在ON后的字段上加索引与否,三者的结果同样.
测试可以放在JOIN的物理操作符上.
0)
DBCC FREEPROCCACHE
GO
DBCC DROPCLEANBUFFERS
GO
1)
SELECT s.v_name,spj.* FROM
(SELECT * FROM spj WHERE qty = 100) AS spj
INNER JOIN s ON s.id = spj.id
OPTION (MERGE JOIN)
--OPTION (HASH JOIN)
--OPTION (LOOP JOIN)