N/APosted on - 10/26/2011
Our professor in Database 2 assigned us to make some small system. We were required to use MS Access as our mode of database storage. Now, after he discussed on what to do, I'm just a little confused between unique constraint and primary key. Is there any differences between these two entity?
UNIQUE constraint and PRIMARY key?
Unique and Primary keys are very confusing but if you look at it in a logical way there are differences in its nature.
For one a primary key cannot be null it can only accept “not null values” while a Unique Key can accept null values. Also in a given table, you can have many unique keys but you can only have one primary key.
Also a Unique key column applies no constrains except for the fact that no duplicates are allowed on that column, while a Primary Key column has a constraint that the value should not be null and that there are no duplicates and an ascending order is followed.