How to count rows in one table based on another table in mysql

Question

I have two tables in a MySQL database. The first one has a list of department names.

departments
    abbreviation | name
    -------------|-------------
             


        

Answer 1

I quick solution, but not the best, could be:

SELECT abbreviation, 
(SELECT COUNT(*) FROM courses C WHERE D.abbreviation = SUBSTRING(C.abbreviation, 0, 3)) AS c 
FROM departments D;