The following SQL Server Not Exists query will find the Employees whose Occupation is neither Skilled Manual nor Clerical.
SELECT E1.EmpID ,E1.Name ,E1.Occupation FROM Employee E1 WHERE NOT EXISTS ( SELECT * FROM Employee E2 WHERE E1.EmpID = E2.EmpID AND Occupation IN ('Skilled Manual', 'Clerical') )
Note: Using NOT EXISTS may have a performance hit. Try to use LEFT JOIN and WHERE column is NULL to test if there is a performance improvement. Sometimes, NOT EXISTS may be faster, and sometimes it may be slower.