在MySql中实现类似row_number，dense_rank，rank函数的排序方法

MySQL中没有Rank排名函数，当需要查询排名时，只能使用MySQL数据库中的基本查询语句来查询普通排名。要在mysql中声明一个变量，必须在变量名之前使用@符号。FROM子句中的(@curRank := 0)部分允许我们进行变量初始化，而不需要单独的SET命令。当然，也可以使用SET

CREATE TABLE `players` (
  `pid` int(2) NOT NULL AUTO_INCREMENT,
  `name` varchar(50) NOT NULL,
  `age` int(2) NOT NULL,
  PRIMARY KEY (`pid`),
  UNIQUE KEY `name` (`name`)
) ENGINE=InnoDB  DEFAULT CHARSET=latin1;

INSERT INTO `players` (`pid`, `name`, `age`) VALUES
(1, 'Samual', 25),
(2, 'Vino', 20),
(3, 'John', 20),
(4, 'Andy', 22),
(5, 'Brian', 21),
(6, 'Dew', 24),
(7, 'Kris', 25),
(8, 'William', 26),
(9, 'George', 23),
(10, 'Peter', 19),
(11, 'Tom', 20),
(12, 'Andre', 20);

1、实现Rank普通排名函数，即row_number()：

SELECT pid, name, age, @curRank := @curRank + 1 AS rank
FROM players p, (
SELECT @curRank := 0
) q
ORDER BY age

SET @curRank := 0;
SELECT pid, name, age, @curRank := @curRank + 1 AS rank
FROM players
ORDER BY age

PID	NAME	AGE	RANK
10	Peter	19	1
12	Andre	20	2
2	Vino	20	3
3	John	20	4
11	Tom	20	5
5	Brian	21	6
4	Andy	22	7
9	George	23	8
6	Dew	24	9
7	Kris	25	10
1	Samual	25	11
8	William	26	12

2、实现Rank普通并列排名函数，即dense_rank():

SELECT pid, name, age, 
	CASE 
        WHEN @prevRank = age THEN @curRank 
        WHEN @prevRank := age THEN @curRank := @curRank + 1
	END AS rank
FROM players p, 
(SELECT @curRank :=0, @prevRank := NULL) r
ORDER BY age

PID	NAME	AGE	RANK
10	Peter	19	1
12	Andre	20	2
2	Vino	20	2
3	John	20	2
11	Tom	20	2
5	Brian	21	3
4	Andy	22	4
9	George	23	5
6	Dew	24	6
7	Kris	25	7
1	Samual	25	7
8	William	26	8

3,实现Rank高级并列排名函数,即rank()函数：

SELECT pid, name, age, rank 
FROM
	(SELECT pid, name, age,
			@curRank := IF(@prevRank = age, @curRank, @incRank) AS rank, 
			@incRank := @incRank + 1, 
			@prevRank := age
	 FROM players p, (
	 SELECT @curRank :=0, @prevRank := NULL, @incRank := 1
	   ) r 
ORDER BY age
  ) s

PID	NAME	AGE	RANK
10	Peter	19	1
12	Andre	20	2
2	Vino	20	2
3	John	20	2
11	Tom	20	2
5	Brian	21	6
4	Andy	22	7
9	George	23	8
6	Dew	24	9
7	Kris	25	10
1	Samual	25	10
8	William	26	12

来源简书：https://www.jianshu.com/p/bb1b72a1623e