stshekhar

 Profile Answers by stshekhar 

• Jun 22nd, 2008

 

One simple diff : there can only one primary key per table but not null+unique can be multiple on one table.

KD09714

 Profile Answers by KD09714 Questions by KD09714

• Jul 1st, 2008

 

1) Primary key creates clustered index by default which actually reorders the row in a table based on index while unique key creates non-clustered index.

2) Replication of table possible only if it contains primary key.

KD09714

 Profile Answers by KD09714 Questions by KD09714

• Jul 1st, 2008

 

1) Primary key creates clustered index by default which actually reorders the row in a table based on index while unique key creates non-clustered index.

2) Replication of table possible only if it contains primary key.    

ashu.gupta

 Profile Answers by ashu.gupta 

• Jul 2nd, 2009

 

Along with the answers mentioned above

To add cascading is only possible when it follow primary key - foriegn key constraint.

Radha

• Jul 14th, 2011

 

We can create NOTNULL and UNIQUE constraints on single column. Which indirectly means a Primary Key.
But only a Primary Key column can be used as Foreign key column.
Primary key provides a default index in it. But we don't have this advantages on the column which we have NOTNULL and Unique Key instead of Primary Key.

PRADEEP

• Oct 17th, 2012

 

Primary key: set of columns is uniquely identified a rows of a table.

It does not allow both nulls and duplicate values.

If we use null values it will allow duplicate values but it does not allow null values.

If we use unique key it does not allow duplicate value but it allows null values.

The main difference is if we use primary key it does not allow both null and duplicate values.