ITPEC FE Morning April 2019 Question 26

SQL MINUS operator — find employees in departments not located in region L2.

Step-by-step:

• •SELECT DNO FROM DEPT → {1, 2, 3}
• •SELECT DNO FROM DEPT_LOCS WHERE Region='L2' → {2, 3}
• •MINUS: {1, 2, 3} - {2, 3} = {1}
• •Final query selects employees where DNO IN (1)

Result: John Bate (20000), Sadat Hossain (50000) → (b)

Why not others:
- (a) NULL/NULL — MINUS does not produce an empty set here; DNO 1 remains
- (c) 4 rows — would require DNO IN (1, 3), but DNO 3 is removed by MINUS
- (d) 5 rows — would mean no filtering at all

Key rule: MINUS (called EXCEPT in standard SQL) returns rows from the first query that do not appear in the second query.

AI-generated — may contain errors