MySQL 用户定义变量和动态列上的 ORDER BY

Question

此查询:

SET @position := 0;
SELECT 
    (@position:=@position + 1),
    (statistics.value - statistics_logs.value) AS value_new
FROM
    rankings AS r
        LEFT JOIN
    rankings_logs AS rl ON statistics_logs.name = statistics.name
        AND statistics_logs.user_id = statistics.user_id
ORDER BY value_new DESC

...没有给出预期的结果:

"(@position := @position + 1)"  value_new
1   10
2   20
3   30
4   40
5   50

相反，它返回奇怪的结果:

"(@position := @position + 1)"  value_new
4   10
2   20
3   30
1   40
5   50

我认为这是因为 value_new 是根据不同表中两个值的提取生成的，并且 ORDER BY 在定义 position 之后以某种方式发生。但我不知道如何解决这个问题。有什么想法吗？

Answer 1

我认为使用子查询会起作用:

SELECT (@position:=@position + 1), value_new
FROM (SELECT (statistics.value - statistics_logs.value) AS value_new
      FROM rankings r LEFT JOIN
           rankings_logs rl
           ON rl.name = r.name AND sl.user_id = s.user_id
      ORDER BY value_new DESC
     ) cross join
     (select @position := 0) vars;