Constraint |
Unique |
Not NULL |
Indexed |
Can Be Referenced |
Multi-Column Constraint |
Can Replace a Rule |
Primary Key |
Yes |
Yes |
Yes |
Yes |
Yes |
Yes |
Foreign Key |
No |
Intended |
Yes |
No |
Yes |
Yes |
Unique Key |
Yes |
Yes |
Yes |
Yes |
Yes |
Yes |
Unique Index |
Yes |
Optional |
Yes |
No |
Yes |
Yes |
Not NULL |
No |
Yes |
No |
No |
No |
Yes |
