mysql分组排序取前n条记录 以及 生成自动数字序列 的sql -- mysql分组排序取前n条记录的最简洁的单条sql。 use test; drop table if exists test; create table test ( id int primary key, cid int, author varchar(30) ) engine=myisam; insert into test v
mysql分组排序取前n条记录 以及 生成自动数字序列 的sql
-- mysql分组排序取前n条记录的最简洁的单条sql。
use test;
drop table if exists test;
create table test (
  id int primary key,
  cid int,
  author varchar(30)
) engine=myisam;
insert into test values  
(1,1,'test1'),
(2,1,'test1'),
(3,1,'test2'),
(4,1,'test2'),
(5,1,'test2'),
(6,1,'test3'),
(7,1,'test3'),
(8,1,'test3'),
(9,1,'test3'),
(10,2,'test11'),
(11,2,'test11'),
(12,2,'test22'),
(13,2,'test22'),
(14,2,'test22'),
(15,2,'test33'),
(16,2,'test33'),
(17,2,'test33'),
(18,2,'test33');
insert into test values  (200,200,'200test_nagios');
select * from (select cid,author,count(*) as number from test group by cid,author) a 
where  
n>(
    select count(*) 
    from (select cid,author,count(*) as number from test group by cid,author) b
    where a.cid=b.cid and a.number)order by cid,number desc;
结果如下：
mysql> select * from (select cid,author,count(*) as number from test group by cid,author) a -> where -> 3>( -> select count(*) -> from (select cid,author,count(*) as number from test group by cid,author) b -> where a.cid=b.cid and a.number )order by cid,number desc;+------+----------------+--------+| cid | author | number |+------+----------------+--------+| 1 | test3 | 4 || 1 | test2 | 3 || 1 | test1 | 2 || 2 | test33 | 4 || 2 | test22 | 3 || 2 | test11 | 2 || 200 | 200test_nagios | 1 |+------+----------------+--------+7 rows in set (0.00 sec)
n就是取分组之后的最前面几个判断，n=3就是取前3个
-- 生成自动数字序列
set @row=0;
select a.*,(@row:=@row +1)rank
from test a;