mysql - Request for the existence of links

Question

How to make a quick selection and get the number of those users who have already invited at least someone?
I tried, suffered, it doesn't work:

SELECT COUNT(u.id) as `count` 
FROM users u 
LEFT JOIN users u1 ON u1.id=u.ref 
LEFT JOIN users u2 ON u2.id=u1.ref

You need to make 1 sql, and it turns out that only the id and ref columns are used.
Those users who haven't invited anyone shouldn't be in the count.

Is it possible to do this or will it be necessary to use cycles and make more requests?

structure is simple - you need to get those who have invited at least someone

For this structure, it should look like this:

1 - invited? Yes!
2 - invited? Yes!
3 - invited? No!
4 - invited? Yes!
5 - invited? Yes!
6 - invited? Yes!
7 - invited? No!

Only 5.

Answer 1

Previous answer was based on an unclear definition of how ref was used. This should give you what you want:

SELECT COUNT(u.id) as `count` 
FROM users u 
WHERE EXISTS (SELECT 1 FROM users u1 WHERE u1.ref = u.id)