Question

I have a two tables accounts and subs.
The first table has id and the second table has fields id, requester_account_id, grabber_account_id

I want the count of how many sub requests an account made, and how many grabs he did (based on if the requester_account_id/grabber_account_id is populated with his id)

In one query

output:

+------------+----------------+-----------------+
| account_id | subs_requested | subs_grabbed    |
+------------+----------------+-----------------+
|  1         | 4              | 3               |
|  3         | 2              | 1               |
+------------+----------------+-----------------+

Answer 1

Use something like

select accounts.id, 
    count(distinct s1.id) as num_req, 
    count(distinct s2.id) as num_grab
from accounts left join subs as s1 on accounts.id = s1.requester_account_id
    left join subs as s2 accounts.id = s2.grabber_account_id
group by accounts.id

The trick is to use table subs twice: subs as s1 and subs as s2, every time joined by different field….

Note regarding efficiency: I’m not sure but I believe this solution is faster than the subquery solution, not tested it though (at least it won’t be slower). I always prefer left join over subquery whenever possible.