mysql：计数和内部联接在同一查询中

Question

I have three tables

users, jobs, proposals

users(id, username, address, email)

jobs(id, title, description, etc)

proposals(id, userid, jobid, date)

A users can apply to many jobs and

a single job can be applied by many users

proposals table stores information of who applied to which job

select j.* from proposals p inner join jobs j on p.jobid = j.id where p.userid=$userid

The above query lists all the jobs applied by the specific user. Now I want to show for each job how many people have applied in same query, is it possible

I tried

 select j.*, count(select * from proposals where jobid =j.id) as count from proposals p inner join jobs j on p.jobid = j.id where p.userid=$userid

also

select j.*, (select count(*) from proposals where jobid =j.id) as count from proposals p inner join jobs j on p.jobid = j.id where p.userid=$userid 

I know the above queries is wrong but this will give some idea.

Answer 1

Isn't group by what you are searching for ?

select j.title, count(*) as number_of_applicants 
from jobs j join proposals 
on j.id = p.jobid 
group by p.jobid;

It might not work perfectly since I don't have the datas to test it, but try on this path !

Answer 2

If you want to use group by , also a subquery is necessary, try following:

select j.*, t.cnt
from jobs j 
join proposals p on p.jobid = j.id
left join (
    select jobid, count(userid) as cnt
    from proposals
    group by jobid
) t on t.jobid = j.id 
where p.userid = $userid

Note: This query may not have better performance than your last query.