mysql分组取每组前几条记录(排名)

 

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+------+------+ | name | val | +------+------+ | a | 2 | | a | 1 | | a | 3 | | b | 5 | | b | 3 | | b | 2 | | b | 4 | | b | 1 | +------+------+

假定使用以下 SQL 进行初始化：

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create table h2yong(name varchar(10),val int); insert into h2yong values('a', 2); insert into h2yong values('a', 1); insert into h2yong values('a', 3); insert into h2yong values('b', 5); insert into h2yong values('b', 3); insert into h2yong values('b', 2); insert into h2yong values('b', 4); insert into h2yong values('b', 1);

按 name 分组取 val 最大的值所在行的数据

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-- 方法1： select a.* from h2yong a where val = (select max(val) from h2yong where name = a.name) order by a.name -- 方法2： select a.* from h2yong a where not exists (select 1 from h2yong where name = a.name and val > a.val) -- 方法3： select a.* from h2yong a,(select name,max(val) val from h2yong group by name) b where a.name = b.name and a.val = b.val order by a.name -- 方法4： select a.* from h2yong a inner join (select name , max(val) val from h2yong group by name) b on a.name = b.name and a.val = b.val order by a.name -- 方法5： select a.* from h2yong a where 1 > (select count(*) from h2yong where name = a.name and val > a.val ) order by a.name

结果如下：

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+------+------+ | name | val | +------+------+ | a | 3 | | b | 5 | +------+------+

按 name 分组取 val 最小的值所在行的数据

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-- 方法1： select a.* from h2yong a where val = (select min(val) from h2yong where name = a.name) order by a.name -- 方法2： select a.* from h2yong a where not exists(select 1 from h2yong where name = a.name and val < a.val) -- 方法3： select a.* from h2yong a,(select name,min(val) val from h2yong group by name) b where a.name = b.name and a.val = b.val order by a.name -- 方法4： select a.* from h2yong a inner join (select name , min(val) val from h2yong group by name) b on a.name = b.name and a.val = b.val order by a.name -- 方法5 select a.* from h2yong a where 1 > (select count(*) from h2yong where name = a.name and val < a.val) order by a.name

结果如下：

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+------+------+ | name | val | +------+------+ | a | 1 | | b | 1 | +------+------+

按 name 分组取第一次出现的行所在的数据

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select a.* from h2yong a where val = (select val from h2yong where name = a.name LIMIT 1) order by a.name

结果如下：

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+------+------+ | name | val | +------+------+ | a | 2 | | b | 5 | +------+------+

按 name 分组随机取一条数据

1	SELECT * FROM (SELECT * FROM h2yong ORDER BY RAND()) as a GROUP BY a.name

结果如下：

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+------+------+ | name | val | +------+------+ | a | 3 | | b | 4 | +------+------+

按 name 分组取最小的两个 (N 个) val

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-- 方法1： select a.* from h2yong a where 2 > (select count(*) from h2yong where name = a.name and val < a.val ) order by a.name,a.val -- 方法2： select a.* from h2yong a where exists (select count(*) from h2yong where name = a.name and val < a.val having Count(*) < 2) order by a.name

结果如下：

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+------+------+ | name | val | +------+------+ | a | 1 | | a | 2 | | b | 1 | | b | 2 | +------+------+

按 name 分组取最大的两个 (N 个) val

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-- 方法1： select a.* from h2yong a where 2 > (select count(*) from h2yong where name = a.name and val > a.val ) order by a.name,a.val -- 方法2： select a.* from h2yong a where exists (select count(*) from h2yong where name = a.name and val > a.val having Count(*) < 2) order by a.name

结果如下：

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+------+------+ | name | val | +------+------+ | a | 2 | | a | 3 | | b | 4 | | b | 5 | +------+------+