sql - How do I combine two LEFT JOINS without getting crossover? -


i've got 2 queries i'd combine one, keep matrix effect when do.

select u.*, count(q.id) users u left join questions q on u.id = q.author_id group u.id

select u.*, count(a.id) users u left join answers on u.id = a.author_id group u.id

those queries give me count of 10 questions , 10 answers. when combine them below, question , answer count jumps 100 each.

select u.*, count(q.id), count(a.id) users u left join questions q on u.id = q.author_id left join answers on u.id = a.author_id group u.id

you need add distinct counts

select u.*, count(distinct q.id), count(distinct a.id)  users u  left join questions q on u.id = q.author_id  left join answers on u.id = a.author_id  group u.id

here's demo of in action using data.se

alternatively can use inline views in clause

select u.*, q.questioncount, a.answercount   users u         left join (select count(id) questioncount,                           author_id                      questions                    group  author_id) q                on u.id = q.author_id         left join (select count(id) answercount,                           author_id                      answers                    group  author_id)                on u.id = q.author_id

demo


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