Mysql 分组排序

DROP TABLE IF EXISTS test;
CREATE TABLE test (
id INT PRIMARY KEY,
cid INT,
author VARCHAR(30)
) ENGINE=INNODB;

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
id,
cid,
author
FROM
(
SELECT
a.id,
a.cid,
a.author,
CASE
WHEN a.cid =@cid
AND a.author =@aut THEN
@x :=@x + 1
ELSE
@x := 1
END AS 'tmp' ,@cid := a.cid ,@aut := a.author,
@x AS r
FROM
test a,
(
SELECT
@x := 1 ,@cid := '' ,@aut := ''
) b
ORDER BY     a.cid,a.author
) tmp
WHERE  r <= 2