reg foreign key relations

[gvraghuramraju]

Is column which "ALLOW NULL" can be a foreign key to other column which is primary key.
IF so how it is possible.

[Lavr]

There are only one restriction for the column which is defined as foreign key:
If the value is other than NULL, it must be from the range of values of the primary key column of the "parent table".
If the value is NULL, it means that such record has no related records in the "parent table".
So all you have to do is to define the column as foreign key and as null.