匿名通过本文主要向大家介绍了MySQL，分组排序，自动数字序列等相关知识,希望本文的分享对您有所帮助
-- 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;
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，更多相关内容请关注微课江湖（）！