Given a table customer holding customers information and the referee.
+------+------+-----------+
| id | name | referee_id|
+------+------+-----------+
| 1 | Will | NULL |
| 2 | Jane | NULL |
| 3 | Alex | 2 |
| 4 | Bill | NULL |
| 5 | Zack | 1 |
| 6 | Mark | 2 |
+------+------+-----------+
Write a query to return the list of customers NOT referred by the person with id '2'.
For the sample data above, the result is:
+------+
| name |
+------+
| Will |
| Jane |
| Bill |
| Zack |
+------+
note: 要用 is Null 和 != .
Code
SELECT name FROM customer WHERE referee_id != 2 OR referee_id IS NULL