Foreign keys and updates
There are other ways of ensuring referential integrity.
SET NULL
delete from P where p_id = 3;
P
| p_id |
x |
| 1 | 123 |
| 2 | 456 |
| 3 | 789 |
| 4 | 111 |
|
|
F
| f_id |
p_id |
y |
| 1001 | 1 | 999 |
| 1002 | 1 | 888 |
| 2001 | 2 | 777 |
| 3001 | 3 | 666 |
| 3002 | 3 | 555 |
| 3003 | 3 | 444 |
|
|
→ |
|
P
|
|
F
| f_id |
p_id |
y |
| 1001 | 1 | 999 |
| 1002 | 1 | 888 |
| 2001 | 2 | 777 |
| 3001 | NULL | 666 |
| 3002 | NULL | 555 |
| 3003 | NULL | 444 |
|
|
|