primary key and unique key in sql which is better

Question

primary key and unique key in sql which is better. Please give me a example. Its very urgent.

Ranjit Powar · Answer

If you want to store null value in your column then use unique key. But only one null value is stored. If you use primary key then you are not able to insert null value.

Sibeesh Venu · Answer

The only difference is unique can contain one null value where as primary key cannot contain any null. Unique Example: 1 2 NULL 3 4 NULL (This will throw constraint violation error as it will be duplicate) 4 (This will also throw constraint violation error as it will be duplicate) Primary key Example: 1 2 NULL (This will throw constraint violation error) 3 4 4 (This will also throw constraint violation error as it will be duplicate) And it is always based on your requirement . Please read here for more info http://www.programmerinterview.com/index.php/database-sql/differences-between-primary-and-foreign-keys/ Please accept and up vote Kindest Regards Sibeesh http://sibeeshpassion.com/