列必须出现在嵌套查询中的分组依据或聚合函数中

Question

我有以下 table.

Fights (fight_year, fight_round, winner, fid, city, league)

我正在尝试查询以下内容：

对于战斗 table 中出现的每一年，找到举行最多战斗的城市。例如，如果在 1992 年，泽西岛举行的比赛比任何其他城市都多，您应该打印出 (1992, Jersey)

这是我目前的情况，但我不断收到以下错误。我不确定我应该如何按功能构建我的组。

错误：列，'ans.fight_round' 必须出现在 GROUP BY 子句中或在聚合函数中使用。第 3 行来自 (select *

select fight_year, city, max(*)
from (select *
    from (select *
        from fights as ans
        group by (fight_year)) as l2
     group by (ans.city)) as l1;

Answer 1

在 Postgres 中，我会推荐聚合和 distinct on:

select distinct on (flight_year) flight_year, city, count(*) cnt
from flights
group by flight_year, city
order by flight_year, count(*) desc

统计每个城市每年打架次数，保留每年打架次数最多的城市。

如果你想允许平局，那么使用window函数：

select flight_year, city, cnt
from (
    select flight_year, city, count(*) cnt,
        rank() over(partition by flight_year order by count(*) desc) rn
    from flights
    group by flight_year, city
) f
where rn = 1

Answer 2

尽管 row_number 是@GMB 所做的最简单的方法。也可以试试这个替代方案

select city, fight_year
from fights 
group by city, fightyear 
having count(*) = sum(case when fid is not null then 1 end)

列必须出现在嵌套查询中的分组依据或聚合函数中

Column must appear in group by or aggregate function in nested query

sql

postgresql

count

sql-order-by

greatest-n-per-group