mysql - 如何在子查询 WHERE 子句中重用变量？

Question

我有一个表格，其中包含每个用户的平均结果。 我想找出平均结果更好的用户百分比。

如果您是 20 位用户中的第五位用户，则 20% 的用户的平均结果更好。

average_results 
+---------+----------------+
| user_id | average_result |
+---------+----------------+
|       1 | 1.0000         |
|       3 | 0.3333         |
+---------+----------------+

这是我正在使用的查询。 当我用 0.3333 对 @user_result 进行硬编码时，它可以工作，但是当我不这样做时，它就不起作用，正如您在 position 和 位置2

SELECT @user_result, position, position2, total, position/total 
FROM 
(
   SELECT @user_result := average_result 
   FROM average_results 
   WHERE user_id = 3  
) as T0,
(
   SELECT COUNT(average_result) as position  
   FROM average_results
   where average_result > @user_result
) AS T1,
(
   SELECT COUNT(average_result) as position2
   FROM average_results
   where average_result > 0.3333
) AS T12,
(
   SELECT COUNT(average_result) as total  
   FROM average_results
) AS T2

Expected output

+--------------+----------+-----------+-------+----------------+
| @user_result | position | position2 | total | position/total |
+--------------+----------+-----------+-------+----------------+
| 0.3333       |        1 |         1 |     2 | 0.5000         |
+--------------+----------+-----------+-------+----------------+

Actual output

+--------------+----------+-----------+-------+----------------+
| @user_result | position | position2 | total | position/total |
+--------------+----------+-----------+-------+----------------+
| 0.3333       |        0 |         1 |     2 | 0.0000         |
+--------------+----------+-----------+-------+----------------+

Answer 1

我会建议如下内容，它不会回答您关于变量的实际问题，但我认为可以满足您的要求。

SELECT t.*, position/total
FROM
(
 SELECT 
  ar2.average_result as user_result,
  SUM(CASE WHEN ar1.average_result > ar2.average_result THEN 1 ELSE 0 END) as position,
  COUNT(*) as total
 FROM average_results ar1 INNER JOIN average_results ar2
  ON ar2.user_id = 3
) t

这是一个 sqlfiddle of it working .