Question

Assuming I have 3 tables:

People
-------------
PID   |  NAME
-------------
1       Bob
2       Garry
3       Alex
4       Peter
5       Victor

Tasks
-------------
TID   |  TASK
-------------
1       Work
2       Work Hard
3       Work Harder

And table that assigns tasks to people

Assigns
-------------
PID   |  TID
-------------
1       2
2       1
4       3

Question:
How do I select People who were not assigned to any task?

Answer 1

The LEFT JOIN approach will work, but here are two more approaches that you might find easier to read:

1. NOT IN

SELECT NAME
FROM People
WHERE PID NOT IN
(
    SELECT PID
    FROM Assigns
)

2. NOT EXISTS

SELECT NAME
FROM People
WHERE NOT EXISTS
(
    SELECT *
    FROM Assigns
    WHERE People.PID = Assigns.PID
)

Result

Alex
Victor

Related

• NOT IN vs. NOT EXISTS vs. LEFT JOIN / IS NULL: Oracle