Question

Each user HAS MANY photos and HAS MANY comments. I would like to order users by

SUM(number_of_photos, number_of_comments)

Can you suggest me the SQL query?

Answer 1

GROUP BY with JOINs works more efficiently than dependent subqueries (in all relational DBs I know):

Select * From Users
Left Join Photos On (Photos.user_id = Users.id)
Left Join Comments On (Comments.user_id = Users.id)
Group By UserId
Order By (Count(Photos.id) + Count(Comments.id))

with some assumptions on the tables (e.g. an id primary key in each of them).