SQL query for not in set?

Question

MySQL

The people help with request (mysql).
Table of applications, Table of photos on applications.
I need to list the numbers of those orders that are not in the table with photos (i.e. I need a list of orders that do not have photos)
I do something like:
SELECT num FROM customerequipment WHERE num NOT IN (SELECT OrderID from attaches).
But returns null

Answer 1

As an option:

SELECT
    num
FROM customerequipment m
WHERE NOT EXISTS (
   SELECT
        1
   FROM attaches e
   WHERE e.OrderID = m.num
)