MySQL group sorting to get the first N records and generate automatic number sequence SQL

--MySQL group sorting takes the simplest single SQL of the first N records.


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;

The results are as follows:

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 is to take the first few judgments after grouping, N=3 is to take the first 3

##--Generate automatic number sequence

SET @ROW=0;
SELECT a.*,(@ROW:=@ROW +1)Rank
FROM test a;

The above is the SQL content of MySQL group sorting, fetching the first N records and generating automatic number sequence. For more related content, please pay attention to the PHP Chinese website (www.php.cn)!