SQL查询语句优化的一点

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(1)INSERT[INTO]BSELECT id,field1,field2 FROMAWHERENOTEXISTS(SELECT idFROMBWHEREid=[A.]id) 

(2)INSERT[INTO]BSELECT*FROMAWHEREidNOTIN(SELECTidFROMB)

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这两句,都是将A表中存在,但B表中不存在的数据,插入到B表中,关联比较字段为id.
但这两句的执行效率,却是有数量级的差别.

结论有两点:
尽量用EXISTS和NOTEXISTS代替IN和NOTIN不要偷懒,尽量不用SELECT*FROM....,而要写字段名SELECTfield1,field2,.... 
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