Question

可能重复：
SQL: Select first row in each GROUP BY group?

两个SQL表。一位参赛者有很多参赛作品：

Contestants     Entries
Id   Name       Id  Contestant_Id  Score
--   ----       --  -------------  -----
1    Fred       1   3              100
2    Mary       2   3              22
3    Irving     3   1              888
4    Grizelda   4   4              123
                5   1              19
                6   3              50

低分获胜。需要检索按分数排序的所有参赛者的当前最佳分数：

Best Entries Report
Name     Entry_Id  Score
----     --------  -----
Fred     5         19
Irving   2         22
Grizelda 4         123

我当然可以通过许多查询完成此操作。我的问题是，是否有办法通过一个有效的SQL查询获得结果。我几乎可以看到如何使用GROUP BY，但不完全。

如果它是相关的，环境是Rails ActiveRecord和PostgreSQL。

Answer 1

最简单的方法是使用排名功能：

select name, Entry_id, score
from (select e.*, c.name,
             row_number() over (partition by e.contestant_id order by score) as seqnum
      from entries e join
           contestants c
           on c.Contestant_id = c.id
     ) ec
where seqnum = 1

Answer 2

我对PostgreSQL并不熟悉，但这些内容应该有效：

SELECT c.*, s.Score
FROM Contestants c
JOIN (SELECT MIN(Score) Score, Contestant_Id FROM Entries GROUP BY Contestant_Id) s
ON c.Id=s.Contestant_Id

Answer 3

其中一个解决方案是

select min(e.score),c.name,c.id from entries e
inner join contestants c on e.contestant_id = c.id
group by e.contestant_id,c.name,c.id

这是一个例子 http://sqlfiddle.com/#!3/9e307/27

Answer 4

这个简单的查询应该可以解决问题..

Select contestants.name as name, entries.id as entry_id,  MIN(entries.score) as score
FROM entries
JOIN contestants ON contestants.id = entries.contestant_id
GROUP BY name
ORDER BY score

这会抓住每个参赛者的最低分数并命令他们ASC

Answer 5

这是具体的postgresql方式：

SELECT DISTINCT ON (c.id) c.name, e.id, e.score
FROM Contestants c
JOIN Entries e ON c.id = e.Contestant_id
ORDER BY c.id, e.score

DISTINCT ON的详细信息为here。

我的SQLFiddle示例。

UPD按分数订购结果：

SELECT *
FROM (SELECT DISTINCT ON (c.id) c.name, e.id, e.score
      FROM Contestants c
      JOIN Entries e ON c.id = e.Contestant_id
      ORDER BY c.id, e.score) t
ORDER BY score

在SQL连接结果中查找组最大值

5 个答案: