SQL Subqueries Filter query results using query on different table
Example
This query selects all employees not on the Supervisors table.
SELECT *
FROM Employees
WHERE EmployeeID not in (SELECT EmployeeID
FROM Supervisors)
The same results can be achieved using a LEFT JOIN.
SELECT *
FROM Employees AS e
LEFT JOIN Supervisors AS s ON s.EmployeeID=e.EmployeeID
WHERE s.EmployeeID is NULL
