Question

I have a SQL Database with 3 tables:

table1: user

id | nickname
1    peter
2    tom

table2: posts

user_id | title | text
1         hmmm    bla
1         yeah    blub
2         blub    dada
1         yuhu    asdf

table3: messages

user_id | title | message
1         hello   bla
2         hi      blub
2         hey     dada
2         huhu    asdf

How do I count every entry from posts/messages for each user in one query?

Answer 1

Try this:

SELECT a.user_id, 
       COALESCE(b.cnt_b, 0) posts_count, 
       COALESCE(c.cnt_c, 0) messages_count
  FROM user a LEFT JOIN 
            (
                SELECT user_id, COUNT(1) cnt_b
                    FROM posts b 
                 GROUP BY user_id
            ) b
     ON a.user_id = b.user_id LEFT JOIN
            (
                SELECT user_id, COUNT(1) cnt_c
                    FROM messages c 
                 GROUP BY user_id
            ) c
    ON a.user_id = c.user_id