Mysql 如何将聚合查询与不同的联接组合起来？

我一直在研究和，试图找出如何在MySQL中进行组合聚合，但运气不太好

以下是我的两个问题：

select a.IsTestAgency, a.ID, a.AgencyName, a.CreateDate, count(*) AS Agents
from Users u
join Agencies a
on u.AgencyID = a.ID
group by a.IsTestAgency, a.ID, a.AgencyName, a.CreateDate
order by a.IsTestAgency, a.AgencyName;

结果:

以及：

结果:

您可以看到列和列的数据类型匹配。我想将它们组合到一个查询中，并排显示

代理

计数和

证书

计数，因为这是结果集中唯一两个不同的列值

怎么做的？这是你想要的吗

select a.*, 
       (select count(*)
        from users u
        where u.AgencyID = a.ID
       ) as users_count,
       (select count(*)
        from Certificates c
        where c.AgencyID = a.ID
       ) as certificates_count
from Agencies a
order by a.IsTestAgency, a.AgencyName;

---

您可以通过

JOIN

ing到

COUNT

s的表来实现这一点：

select a.IsTestAgency, a.ID, a.AgencyName, a.CreateDate, u.Agents, c.Certs
from Agencies a
join (select AgencyID, COUNT(*) as Agents from Users group by AgencyID) u on u.AgencyID = a.ID
join (select AgencyID, COUNT(*) as Certs from Certficates group by AgencyID) c on c.AgencyID = a.ID
order by a.IsTestAgency, a.AgencyName;

---

这样就不需要在顶部查询中按分组，也不用为输出的每一行进行两个子查询计数。

@BobJarvis。一点也不。那不应该在那里。

select a.IsTestAgency, a.ID, a.AgencyName, a.CreateDate, u.Agents, c.Certs
from Agencies a
join (select AgencyID, COUNT(*) as Agents from Users group by AgencyID) u on u.AgencyID = a.ID
join (select AgencyID, COUNT(*) as Certs from Certficates group by AgencyID) c on c.AgencyID = a.ID
order by a.IsTestAgency, a.AgencyName;