Can Foreign Key be null?
158985
Can a foreign key be NULL and/or duplicate?
18217
Does Foreign Key improve query performance?
99717
Foreign key constraint on array member?
144063
Error Code: 1215. Cannot add foreign key constraint (foreign keys)
47887
NULL values in where clause
41165
Foreign key constraints failures
85789
Not using foreign key constraints in real practice. Is it OK?
656
Foreign key constraint error 1452 in MySQL - Magento import
72088
Why shouldn't we allow NULLs?
89949
Easy mysql question regarding primary keys and an insert
134955
Foreign key issue:ERROR 1005 (HY000): Can't create table (errno: 150)
90352
android sqlite foreign key not working
20394
Renaming foreign-key columns in MySQL
46729
Add non-nullable columns to an existing table in SQL server?
28648
Will new return NULL in any case?
97261
Are nested transactions allowed in MySQL?
149602
One to at most one relation or multiple null columns?