There is 2 table: "users" and "clicks".
Users have: 'username' and 'referrer'
Clicks have: 'user' and 'value'
users.username = clicks.user
How can I SUM clicks.value of the users whos referrer is "janosuser"?
I know it's INNER Join but I don't know what is the sql.
When you are not sure whether the username in users table is unique or not
SELECT sum(clicks.value) FROM clicks WHERE clicks.user IN (SELECT users.username from users WHERE users.referrer = "janosuser")
When you are sure that users table doesn't have repeated username, i.e. username is unique in the users table, otherwise for that users there will be repeated rows and sum will be inflated
SELECT SUM(clicks.value) FROM clicks INNER JOIN users ON users.username = clicks.user where users.refere = "janosuser"