Mariadb（MYSQL）窗口函數-排序

測試表test

class	name	score
1	張一	100
1	張二	99
1	張三	99
1	張四	98
1	張五	97
2	李一	100
2	李二	99
2	李三	98
2	李四	97
2	李五	96

排序（rank，dense_rank）

在 8.0 版本之前,參考了https://segmentfault.com/q/1010000011138138

1. 使用臨時變量

-- 變量爲session級別，執行多次變量會累加，需要使用select @x:=0;將變量置0 
SELECT
	@x := ifnull( @x, 0 ) + 1 AS rownum,
	score 
FROM
	test 
ORDER BY
	score DESC;

2.使用笛卡兒積

SELECT
	a.NAME,
	a.score,
	count( * ) AS rownum 
FROM
	test a,
	test b 
WHERE
	a.score <= b.score 
GROUP BY
	a.NAME,
	a.score 
ORDER BY
	count( * ) ASC;

3. 使用子查詢

SELECT
	a.*,
	( SELECT count( * ) FROM test WHERE score >= a.score ) AS rownum 
FROM
	test a 
ORDER BY
	rownum ASC;

MySQL 8.0版本後

使用窗口函數不僅可以整體排序，還可以局部排序

-- 整體排序
SELECT
	class,
	score,
	NAME,
	rank() over ( ORDER BY score DESC ) AS rownum 
FROM
	test 
ORDER BY
	rownum;

-- 每個班級內部排名--RANK,相同值相同排名，排名不連續
SELECT
	class,
	score,
	NAME,
	RANK() over (PARTITION by class ORDER BY score DESC ) AS rownum 
FROM
	test 
ORDER BY
	class,rownum;

-- 每個班級內部排名--DENSE_RANK,相同值相同排名，排名連續
SELECT
	class,
	score,
	NAME,
	DENSE_RANK() over (PARTITION by class ORDER BY score DESC ) AS rownum 
FROM
	test 
ORDER BY
	class,rownum;

-- 每個班級內部排名--DENSE_RANK,相同值相同不同，排名連續
SELECT
	class,
	score,
	NAME,
	ROW_NUMBER() over (PARTITION by class ORDER BY score DESC ) AS rownum 
FROM
	test 
ORDER BY
	class,rownum;