如何在一个查询中根据另一个表中的 id 计算两个不同表中的值？

Question

I'm looking to count the amount of users and channel_memberships that have a channel_partner_id for each channel from the channel_partners table.

I want to run these two queries in one query:

SELECT channel_partners.id,
    channel_partners.name,
    COUNT(channel_memberships.channel_partner_id) AS membership_count
    
FROM channel_partners
JOIN channel_memberships ON channel_partners.id = channel_memberships.channel_partner_id

GROUP BY channel_partners.id 

and

SELECT channel_partners.id,
    channel_partners.name,
    COUNT(users.channel_partner_id) AS user_count
    
FROM channel_partners
JOIN users ON channel_partners.id = users.channel_partner_id

GROUP BY channel_partners.id

I've tried to do this:

SELECT channel_partners.id,
    channel_partners.name,
    COUNT(users.channel_partner_id) AS user_count,
    COUNT(channel_memberships.channel_partner_id) AS membership_count
    
FROM channel_partners
JOIN users ON channel_partners.id = users.channel_partner_id 
JOIN channel_memberships ON channel_partners.id = channel_memberships.channel_partner_id


GROUP BY channel_partners.id

When I run this both user_count and membership_count are equal and have values that are vastly different from when I run the two queries individually. For example when ran individually, for the channel_partner with id 20 I get 1178 user_count, 12588 membership_count, and when I run both together I get user_count and membership_count equaling 14828664 for the channel_partner with id 20.

Answer 1

Thanks for Martin and Nick in the comments for helping me solve this. I can use subqueries instead of joins.

This is the working query here:

SELECT channel_partners.id,
    channel_partners.name,
    (SELECT COUNT(users.channel_partner_id)
        FROM users
        WHERE users.channel_partner_id = channel_partners.id) AS user_count,
    (SELECT COUNT(channel_memberships.channel_partner_id)
        FROM channel_memberships
        WHERE channel_memberships.channel_partner_id = channel_partners.id) AS membership_count
    
FROM channel_partners