MySQL 通过 rand() 将 order 修改为其他方法

Question

我现在尝试从每个分组的列数组中进行随机选择，机会后面是每行的权重。例如，我有一个这样的表（DemoTable）： http://sqlfiddle.com/#!9/23470/3/0

Name	State	Grade	Weight
John	NY	100	1
Liam	NY	90	2
Olivia	NY	90	3
Emma	NY	80	4
James	CA	10	1
Henry	CA	20	1
Mia	NJ	50	1
Ava	NJ	30	4

对于 State = 'NY'，有四行带有等级数组：[100, 90, 90, 80] 和权重 [1, 2, 3, 4]，分别。因此，在其州组中，80 人被选中的机会最大，而 100 人被选中的机会最少。 我查询了它：

SELECT a.*,
(SELECT b.Grade FROM DemoTable b WHERE a.State = b.State 
ORDER BY RAND() * -b.Weight LIMIT 1) AS 'random_val' FROM DemoTable a;

它与结果一起工作：

Name	State	Grade	Weight	random_val
John	NY	100	1	80
Liam	NY	90	2	80
Olivia	NY	90	3	80
Emma	NY	80	4	90
James	CA	10	1	20
Henry	CA	20	1	10
Mia	NJ	50	1	30
Ava	NJ	30	4	30

不过，我想知道是否有其他方法，例如 join 或 union，而不是单独使用 order by rand()。
有没有其他方法可以修改我的 MySQL 查询以提供相同的结果？
我整天都在寻找解决这个问题的方法，但找不到正确的方法；这就是我在这里寻求帮助的原因。
如果我能得到一些建议，我将不胜感激。

Answer 1

我第一次尝试使用分析函数，虽然我怀疑你的比更大的数据集更快...

WITH
  ranged AS
(
  SELECT
    *,
    SUM(weight) OVER (PARTITION BY state ORDER BY id) - weight   AS weight_range_lower,
    SUM(weight) OVER (PARTITION BY state ORDER BY id)            AS weight_range_upper,
    SUM(weight) OVER (PARTITION BY state            ) * rand()   AS rand_threshold
  FROM
    DemoTable
)
SELECT
  ranged.*,
  lookup.grade   AS random_grade
FROM
  ranged
INNER JOIN
  ranged  AS lookup
    ON  lookup.state               = ranged.state
    AND lookup.weight_range_lower <= ranged.rand_threshold
    AND lookup.weight_range_upper >  ranged.rand_threshold
ORDER BY
  ranged.id

或者，如果您希望同一状态的所有成员都获得相同的 random_grade...

SELECT
  *,
  FIRST_VALUE(grade) OVER (PARTITION BY state ORDER BY weight * rand() DESC)
FROM
  DemoTable
ORDER BY
  id

https://dbfiddle.uk/?rdbms=mysql_8.0&fiddle=133f9e86b013a477ac342d0295132dd5