sql 如何理解
select a.user_name,a.over,(select over from user2 b where a.user_name=b.user_name) as over2 from user1 a; 这个sql怎么理解呢？
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select a.user_name,a.over,(select over from user2 b where a.user_name=b.user_name) as over2 from user1 a; 这个sql怎么理解呢？
2016-01-14
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