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<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;