[转] mysql分组取每组前几条记录(排名)_MySQL

--按某一字段分组取最大(小)值所在行的数据

/*<br>数据如下：<br>name val memo<br>a    2   a2(a的第二个值)<br>a    1   a1--a的第一个值<br>a    3   a3:a的第三个值<br>b    1   b1--b的第一个值<br>b    3   b3:b的第三个值<br>b    2   b2b2b2b2<br>b    4   b4b4<br>b    5   b5b5b5b5b5<br>*/

--创建表并插入数据：

create table tb(name varchar(10),val int,memo varchar(20))<br>insert into tb values('a',    2,   'a2(a的第二个值)')<br>insert into tb values('a',    1,   'a1--a的第一个值')<br>insert into tb values('a',    3,   'a3:a的第三个值')<br>insert into tb values('b',    1,   'b1--b的第一个值')<br>insert into tb values('b',    3,   'b3:b的第三个值')<br>insert into tb values('b',    2,   'b2b2b2b2')<br>insert into tb values('b',    4,   'b4b4')<br>insert into tb values('b',    5,   'b5b5b5b5b5')<br>go

--一、按name分组取val最大的值所在行的数据。

--方法1：<br>select a.* from tb a where val = (select max(val) from tb where name = a.name) order by a.name<br>--方法2：<br>select a.* from tb a where not exists(select 1 from tb where name = a.name and val &gt; a.val)<br>--方法3：<br>select a.* from tb a,(select name,max(val) val from tb group by name) b where a.name = b.name and a.val = b.val order by a.name<br>--方法4：<br>select a.* from tb a inner join (select name , max(val) val from tb group by name) b on a.name = b.name and a.val = b.val order by a.name<br>--方法5<br>select a.* from tb a where 1 &gt; (select count(*) from tb where name = a.name and val &gt; a.val ) order by a.name<br>/*<br>name       val         memo                <br>---------- ----------- --------------------<br>a          3           a3:a的第三个值<br>b          5           b5b5b5b5b5<br>*/

--二、按name分组取val最小的值所在行的数据。

--方法1：<br>select a.* from tb a where val = (select min(val) from tb where name = a.name) order by a.name<br>--方法2：<br>select a.* from tb a where not exists(select 1 from tb where name = a.name and val --方法3：<br>select a.* from tb a,(select name,min(val) val from tb group by name) b where a.name = b.name and a.val = b.val order by a.name<br>--方法4：<br>select a.* from tb a inner join (select name , min(val) val from tb group by name) b on a.name = b.name and a.val = b.val order by a.name<br>--方法5<br>select a.* from tb a where 1 &gt; (select count(*) from tb where name = a.name and val /*<br>name       val         memo                <br>---------- ----------- --------------------<br>a          1           a1--a的第一个值<br>b          1           b1--b的第一个值<br>*/

--三、按name分组取第一次出现的行所在的数据。

select a.* from tb a where val = (select top 1 val from tb where name = a.name) order by a.name<br>/*<br>name       val         memo                <br>---------- ----------- --------------------<br>a          2           a2(a的第二个值)<br>b          1           b1--b的第一个值<br>*/

--四、按name分组随机取一条数据。

select a.* from tb a where val = (select top 1 val from tb where name = a.name order by newid()) order by a.name<br>/*<br>name       val         memo                <br>---------- ----------- --------------------<br>a          1           a1--a的第一个值<br>b          5           b5b5b5b5b5<br>*/

--五、按name分组取最小的两个(N个)val

select a.* from tb a where 2 &gt; (select count(*) from tb where name = a.name and val select a.* from tb a where val in (select top 2 val from tb where name=a.name order by val) order by a.name,a.val<br>select a.* from tb a where exists (select count(*) from tb where name = a.name and val /*<br>name       val         memo                <br>---------- ----------- --------------------<br>a          1           a1--a的第一个值<br>a          2           a2(a的第二个值)<br>b          1           b1--b的第一个值<br>b          2           b2b2b2b2<br>*/

--六、按name分组取最大的两个(N个)val

select a.* from tb a where 2 &gt; (select count(*) from tb where name = a.name and val &gt; a.val ) order by a.name,a.val<br>select a.* from tb a where val in (select top 2 val from tb where name=a.name order by val desc) order by a.name,a.val<br>select a.* from tb a where exists (select count(*) from tb where name = a.name and val &gt; a.val having Count(*) /*<br>name       val         memo                <br>---------- ----------- --------------------<br>a          2           a2(a的第二个值)<br>a          3           a3:a的第三个值<br>b          4           b4b4<br>b          5           b5b5b5b5b5<br>*/

--七，假如整行数据有重复，所有的列都相同。

/*<br>数据如下：<br>name val memo<br>a    2   a2(a的第二个值)<br>a    1   a1--a的第一个值<br>a    1   a1--a的第一个值<br>a    3   a3:a的第三个值<br>a    3   a3:a的第三个值<br>b    1   b1--b的第一个值<br>b    3   b3:b的第三个值<br>b    2   b2b2b2b2<br>b    4   b4b4<br>b    5   b5b5b5b5b5<br>*/

--在sql server 2000中只能用一个临时表来解决，生成一个自增列，先对val取最大或最小，然后再通过自增列来取数据。

--创建表并插入数据：

create table tb(name varchar(10),val int,memo varchar(20))<br>insert into tb values('a',    2,   'a2(a的第二个值)')<br>insert into tb values('a',    1,   'a1--a的第一个值')<br>insert into tb values('a',    1,   'a1--a的第一个值')<br>insert into tb values('a',    3,   'a3:a的第三个值')<br>insert into tb values('a',    3,   'a3:a的第三个值')<br>insert into tb values('b',    1,   'b1--b的第一个值')<br>insert into tb values('b',    3,   'b3:b的第三个值')<br>insert into tb values('b',    2,   'b2b2b2b2')<br>insert into tb values('b',    4,   'b4b4')<br>insert into tb values('b',    5,   'b5b5b5b5b5')<br>go<br>select * , px = identity(int,1,1) into tmp from tb<br>select m.name,m.val,m.memo from<br>(<br>select t.* from tmp t where val = (select min(val) from tmp where name = t.name)<br>) m where px = (select min(px) from<br>(<br>select t.* from tmp t where val = (select min(val) from tmp where name = t.name)<br>) n where n.name = m.name)<br>drop table tb,tmp<br>/*<br>name       val         memo<br>---------- ----------- --------------------<br>a          1           a1--a的第一个值<br>b          1           b1--b的第一个值<br>(2 行受影响)<br>*/

--在sql server 2005中可以使用row_number函数，不需要使用临时表。

--创建表并插入数据：

create table tb(name varchar(10),val int,memo varchar(20))<br>insert into tb values('a',    2,   'a2(a的第二个值)')<br>insert into tb values('a',    1,   'a1--a的第一个值')<br>insert into tb values('a',    1,   'a1--a的第一个值')<br>insert into tb values('a',    3,   'a3:a的第三个值')<br>insert into tb values('a',    3,   'a3:a的第三个值')<br>insert into tb values('b',    1,   'b1--b的第一个值')<br>insert into tb values('b',    3,   'b3:b的第三个值')<br>insert into tb values('b',    2,   'b2b2b2b2')<br>insert into tb values('b',    4,   'b4b4')<br>insert into tb values('b',    5,   'b5b5b5b5b5')<br>go<br>select m.name,m.val,m.memo from<br>(<br>select * , px = row_number() over(order by name , val) from tb<br>) m where px = (select min(px) from<br>(<br>select * , px = row_number() over(order by name , val) from tb<br>) n where n.name = m.name)<br>drop table tb<br>/*<br>name       val         memo<br>---------- ----------- --------------------<br>a          1           a1--a的第一个值<br>b          1           b1--b的第一个值<br>(2 行受影响)<br>*/