Can a database table contains more than one primary key?

Question

Can a database table contains more than one primary key?

Yes, I am talking about RDBMS.

Answer 1

A table can have:

• No primary keys;
• One primary key consisting of one column; or
• One composite primary key consisting of two or more columns.

Other than that you can have any number of unique indexes, which will do basically the same thing.

Answer 2

The primary key of a relational table uniquely identifies each record in the table. So, in order to keep the uniqueness of each record, you cant have more than one primary key for the table. It can either be a normal attribute that is guaranteed to be unique (such as Social Security Number in a table with no more than one record per person) or it can be generated by the DBMS (such as a globally unique identifier, or GUID, in Microsoft SQL Server). Primary keys may consist of a single attribute or multiple attributes in combination.

Answer 3

That's why it is called Primary Key because it is, well, PRIMARY

Answer 4

Yes, you can have Composite primary keys, that is, having two fields as a primary key.