一个有趣的SQL查询CHALLENGE - 列出每位运动员前3名的AVERAGE值

Question

An interesting SQL query CHALLENGE:

A table named athelets consisting of id, ath_id, name, score, date.

+----+--------+-----------------+--------+------------+
| id | ath_id | name            | record | r_date     |
+----+--------+-----------------+--------+------------+
|  1 |      2 | John Wayne      |     79 | 2010-07-08 |
|  2 |      7 | Ronald Regan    |     51 | 2000-03-22 |
|  3 |      1 | Ford Harrison   |     85 | 2009-11-13 |
|  4 |      2 | John Wayne      |     69 | 2017-01-01 |

Please write a sql query to list the average value of the top three scores of each athlete, something like:

ath_id: 1, the arithmetic mean of his/her top 3 records: 77
ath_id: 2, the arithmetic mean of his/her top 3 records: 73
ath_id: 3, the arithmetic mean of his/her top 3 records: 47

Answer 1

SELECT p.id
,coalesce(c.comment_count,0) as comment_count
,coalesce(f.favorite_count,0) as favorite_count
FROM post p
LEFT JOIN (select post_id,count(*) as comment_count 
           from comment group by post_id) c ON c.post_id=p.id
LEFT JOIN (select post_id,count(*) as favorite_count 
           from favourite group by post_id) f ON f.post_id=p.id

上述查询应该按预期工作。

Answer 2

假设运动员和记录的组合是独一无二的......

SELECT ath_id
     , ROUND(AVG(record),2) top3_avg 
  FROM 
     ( SELECT x.* 
         FROM athletes x 
         JOIN athletes y 
           ON y.ath_id = x.ath_id 
          AND y.record >= x.record 
        GROUP 
           BY x.id 
       HAVING COUNT(*) <=3
     ) a 
 GROUP 
    BY ath_id;