如何编写这些复杂的 MySQL 查询？

Question

我有以下 2 个表：

表'船长'

id	name
1	captain1
2	captain2
3	captain3
4	captain4
5	captain5
6	captain6
7	captain7
8	captain8
9	captain9
10	captain10

表'远征'

id	number	id_captain	id_navire	id_hero
1	1	1	10	8
2	2	2	1	5
3	3	1	8	3
4	4	10	9	6
5	5	5	7	4
6	6	6	5	4
7	7	7	3	7
8	8	8	2	8
9	9	9	1	3
10	10	1	4	2
11	11	6	3	1
12	12	8	6	1
13	13	5	8	6
14	14	4	9	9
15	15	3	10	4
16	16	10	2	2
17	17	9	3	3
18	18	8	7	7
19	19	9	8	10
20	20	7	2	2

我有这个问题：

指导远征最多的船长 在 SQL 中对此进行了处理：

select id_captain, count(expedition.id) as expedition_count
  from expedition
  group by id_captain
  having expedition_count = max(expedition_count);

但没有成功。我期待结果是这样的：

name	expedition_count
captain1	3
captain9	3
captain8	3

Answer 1

这是几个步骤：获取每个字幕的计数，获取最大计数，仅显示最大计数的船长。

一种典型的方法是使用窗口函数（自 MySQL 8 起可用）：

select id_captain, expedition_count
from
(
  select 
    id_captain,
    count(*) as expedition_count,
    max(count(*)) over () as max(expedition_count)
  from expedition
  group by id_captain
) analyzed
where expedition_count = max_expedition_count;

或子查询：

select id_captain, count(*) as expedition_count
from expedition
group by id_captain
having expedition_count = 
(
  select count(*)
  from expedition
  group by id_captain
  order by count(*) desc
  limit 1
);