如何删除表中的记录，该表的主键在另一个表中被引用为外键？

Question

In my database, I have a table say "employee" which has a primary key attribute "employee_id" and another attribute "salary". There is another table say "employee_qualification" which has a foreign key attribute "employee_id". So, how can I delete all the records from "employee" and "employee_qualifications" with salary=10000?

This doesn't seem to work.

DELETE FROM employee WHERE employee.salary=10000;

Answer 1

You can execute two statements.

DELETE FROM employee_qualifications WHERE employee_qualifications.employee_id in (SELECT employee_id FROM employee WHERE employee.salary=10000)
DELETE FROM employee WHERE employee.salary=10000

While this will work, it could leave some orphaned records in the employee_qualifications table. The below option will clean the orphaned records.

DELETE FROM employee WHERE employee.salary=10000
DELETE FROM employee_qualifications WHERE employee_qualifications.employee_id Not in (SELECT employee_id FROM employee)

Answer 2

MySQL allows deletes from multiple tables at the same time. So you can do:

DELETE e, eq
    FROM employee e JOIN
         employee_qualitifications eq
    WHERE e.employee_id = eq.employee_id AND
          e.salary = 10000;