如何将聚合查询与不同联接结合在一起？

Question

I've been looking at this SO post and this jooq.org post , trying to figure out how to do my combined aggregations in MySQL , but not having much luck.

Here are my 2 queries:

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;

Results:

and:

select a.IsTestAgency, a.ID, a.AgencyName, a.CreateDate, count(*) AS Certs
from Certificates c
join Agencies a
on c.AgencyID = a.ID
group by a.IsTestAgency, a.ID, a.AgencyName, a.CreateDate
order by a.IsTestAgency, a.AgencyName;

Results:

You can see that the columns and columns' datatypes match. I'd like to combine these into a single query and show the Agents count and the Certs count side-by-side, since those are the only 2 column values that are different in the result sets.

How is it done?

Answer 1

Is this what you want?

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;

Answer 2

You could do this by JOIN ing to tables of COUNT s:

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;

This removes the need to group by in the top query and also saves having to do two subquery counts for each row of the output.