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;
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