在mySql中获取不同计数的计数

我有两张表，一张是团队的，一张是球员的，我想找出的是总人数表，换句话说，我想计算有2名成员的团队总数，以及有3名成员的团队总数，等等

下面是数据库结构

（侧边栏问题：我是这里的新手：有没有更好的方法发布SQL？）

我想要的是计算团队规模

我希望看到以下输出

Team_Size  Count
1          1
2          2
4          1

---

最简单的方法可能是：

select team_count, count(*) from
(select count(*) team_count from players group by team_id) sq
group by team_count

（虽然这不包括没有球员的球队。）

---

SQLFIDLE。

首先，您需要团队规模：

select t.id as teamId, count(p.id) as teamSize
from 
    `Teams` as t
    left join `Players` as p on t.id = p.teamId
group by
    t.id;

请注意，这将返回零玩家的团队。如果您不想这样做，请使用

内部联接

而不是

左联接

现在，将此查询用作最终查询的行源：

select teamSize, count(teamId)
from (
    select t.id as teamId, count(p.id) as teamSize
    from 
        `Teams` as t
        left join `Players` as p on t.id = p.teamId
    group by
        t.id) as a
group by teamSize;

希望这有帮助

---

还有一件事

如果您有大数据集，此查询可能会挂起。因此，最好创建一个临时表，为其编制索引，并在临时表上运行查询：

drop table if exists temp_teamSize;
create temporary table temp_teamSize
    select t.id as teamId, count(p.id) as teamSize
    from 
        `Teams` as t
        left join `Players` as p on t.id = p.teamId
    group by
        t.id;
alter table temp_teamSize
    add unique index idx_teamId(teamId),
    add index idx_teamSize(teamSize);
select teamSize, count(teamId)
from temp_teamSize
group by teamSize;

---

这是发布SQL的好方法。你也可以在这里设置一个演示（除了在这里发布相关代码）+1这是我在过去几个月里看到的最清晰的问题之一

drop table if exists temp_teamSize;
create temporary table temp_teamSize
    select t.id as teamId, count(p.id) as teamSize
    from 
        `Teams` as t
        left join `Players` as p on t.id = p.teamId
    group by
        t.id;
alter table temp_teamSize
    add unique index idx_teamId(teamId),
    add index idx_teamSize(teamSize);
select teamSize, count(teamId)
from temp_teamSize
group by teamSize;