如何在SQL平均值，然后订单数据，如果它可以在两列中出现？

Question

所以，我有喜欢points列的表person1_id person2_id team_score，你可以看到一个人能在person1_id或person2_id柱出现，因为玩家可以在多个团队，所以这个问题是如何获得最高average_score前n位的球员被定义通过平均所有team_score的他|她参加了？像person_id average_score？

Answer 1

我认为蒂姆的答案是一个很好的答案。但是，假设你有一个persons表，你可以做到这一点没有union all：

select p.person_id,
       (select avg(team_score)
        from points po
        where p.person_id in (po.person1_id, po.person2_id)
       ) as average_score
from persons p
order by average_score desc
limit 5;  -- or whatever

一个较为复杂的表达式可能是最有效的：

select p.person_id,
       ( (select sum(team_score)
          from points po
          where p.person_id = po.person1_id
         ) +
         (select sum(team_score)
          from points po
          where p.person_id = po.person2_id
         )
       ) /
       nullif( (select count(*)
                from points po
                where p.person_id = po.person1_id
               ) +
               (select count(*)
                from points po
                where p.person_id = po.person2_id
               ), 0
             ) as average_score
from persons p
order by average_score desc
limit 5; 

究其原因，这是更有效的是，它可以利用索引对points(person1_id, team_score)和points(person2_id, team_score)。

Answer 2

一种方法是使用一个联合创建的所有球员和他们的分数单一逻辑列：

SELECT
    person_id,
    AVG(team_score) AS average_score
FROM
(
    SELECT person1_id AS person_id, team_score FROM points
    UNION ALL
    SELECT person2_id, team_score FROM points
) t
GROUP BY
    person_id
ORDER BY
    AVG(team_score) DESC
LIMIT 10;   -- e.g. for the top 10, but you may replace 10 with any value you want

Answer 3

你可能会用coalesce功能，可以解决你的问题，是这样的：

SELECT    
  COALESCE(person1_id, person2_id) AS person_id,  
  AVG(team_score) as average_score 
FROM points  
GROUP BY COALESCE(person1_id, person2_id)
ORDER BY AVG(team_score)

这是怎么回事是COALESCE(col1, col2)列表返回第一个非空列。只要你喜欢，你可以尽可能多列做到这一点。

下面是文档：https://www.sqlite.org/lang_corefunc.html#coalesce

Answer 4

首先，你需要得到所有不同的球员，然后将其加入qazxsw点表：

points

见

select 
  d.id person_id, 
  avg(p.team_score) avgscore 
from (
  select person1_id id from points
  union
  select person2_id id from points
) d inner join points p
on (p.person1_id = d.id) or (p.person2_id = d.id)
group by d.id
order by avgscore desc
limit 3