What is the difference between primary key and unique constraints?
Both primary key and unique key enforces uniqueness of the column on which they are defined .
1)But by default , a primary key creates a clustered indexes on the column , whereas unique creates a non clustered index by default .
2) Also, primary key does not allow NULL values , but unique key allows NULL values .
3) There can be more than one unique key for a table but there can not be more than one primary key for a table .
If you don't know what is clustered or non-clustered indexes then See This
Both primary key and unique key enforces uniqueness of the column on which they are defined .
1)But by default , a primary key creates a clustered indexes on the column , whereas unique creates a non clustered index by default .
2) Also, primary key does not allow NULL values , but unique key allows NULL values .
3) There can be more than one unique key for a table but there can not be more than one primary key for a table .
If you don't know what is clustered or non-clustered indexes then See This
No comments:
Post a Comment