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對于SQL的方面，接觸的不多，實(shí)在有種摸不到頭腦的感覺。查看全部
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MySQL不支持full join：查看全部
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select a.user_name,b.timestr,b.kills from suer1 a join user_kills b on a.id=b.user_id where user_name='孫悟空' order by b.kills desc limit 2 可以用sql批量查詢： select d.user_name,timestr,kills,(select count(*) from user_kills b where b.user_id=a.user_id and a.kills<=b.kills) as cnt from suer_kills a group by user_id.timestr.kills) c join user1 d on c.user_id=d.id where cnt<=2查看全部
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select a.user_name,b.timestr,b.kills from user1 a join user_kills b on a.id=b.user_id where b.kills=(select max(c.kills) from user_kills where c.user_id = b.user_id) 優(yōu)化成： select a.user_name,b.timestr,b.kills from user1 a join user_kills b on a.id=b.user_id join user_kills c on c.user_id=b.user_id group by a.user_name,b.timestr,b.kills having b.kills=max(c.kills);查看全部
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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 可優(yōu)化為： select a.user_name,a.over,b.over as over2 from user1 a left join user2 b on a.user_name=b.user_name查看全部
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SQL語句分類 DDL 數(shù)據(jù)定義語言，create alter TPL 事務(wù)處理語言 DCL 數(shù)據(jù)控制語言 DML 數(shù)據(jù)操作語言，insert select update delete查看全部
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SQL語句分類 DDL 數(shù)據(jù)定義語言，create alter TPL 事務(wù)處理語言 DCL 數(shù)據(jù)控制語言 DML 數(shù)據(jù)操作語言，insert select update delete查看全部
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用來標(biāo)記一下查看全部
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分類聚合，在查詢多種分類數(shù)據(jù)時使用到一種聚合方式查看全部
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left outer Join ：結(jié)果集：求出左邊表為主，查詢與左表相同的數(shù)據(jù) 語句：select a.user_name,a.over,b.over from user1 a join user2 b on a.user_name=b.user_name where b.user_name is not null查看全部
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Mysql Full join查看全部
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inner join查看全部
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JOIN類型查看全部
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full join 1查看全部
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Right Outer Join 3查看全部
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