-- 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<b.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<b.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;
以上就是mysql分组排序取前n条记录 以及 生成自动数字序列 的sql的内容。