Question

I’m trying to create an SQL statement that joins two tables and returns a count. I need all the records returning even if there are no items found for the count.

If I just do this:

SELECT s.subject,s2.subject from subjects s 
left join subjects s2 on s.parent_id = s2.id

It’s fine but there’s no count. I tried joining it to the other table I need to do the count on by doing this:

SELECT s.subject,s2.subject,count(q.id) from subjects s 
left join subjects s2 on s.parent_id = s2.id 
join questions q on q.subject_id = s.id

but I just get one result that doesn’t have any meaning at all.

Answer 1

Try this:

 SELECT s.subject, s2.subject, COUNT(q.id) 
 FROM subjects s 
 LEFT JOIN subjects s2 ON s.parent_id  = s2.id 
 LEFT JOIN questions q ON q.subject_id = s.id 
 GROUP BY s.subject_id, s2.subject_id, q.subject_id