Question

I’m working with a SQL database for a Skills Matrix application and I need a query to return a list of employees that are qualified for a given position. Here’s a brief overview of the relevant relationships:

• Employee has many skills through
  qualifications
• Position has many
  skills through requirements

Is there a efficient way to return a list of employees that have the qualifications to meet a certain position’s requirements?

EDIT

employees
- id
- name

positions
- id
- title

skills
- id
- name

requirements
- position_id
- skill_id

qualifications
- employee_id
- skill_id

Answer 1

SELECT *
FROM employees e
WHERE NOT EXISTS (
    SELECT *
    FROM requirements r
    WHERE r.position_id = 1234
    AND NOT EXISTS (
        SELECT *
        FROM qualifications q
        WHERE q.skill_id = r.skill_id
        AND q.employee_id = e.employee_id
    )
)

It will find all employees such that there are no requirement that is not filled by the employee’s qualifications.

The use of nested NOT EXISTS is even mentioned in the MySQL Reference Maual