Can a table have two primary keys?

No. A table can have only one primary key.

However, that primary key can consist of two columns. For example, consider this table of DatabaseProducts:

Company    Product     Release
IBM        DB2         5
Microsoft  SQL Server  7.0
Microsoft  Access      97
Oracle     Oracle      8
Sybase     ASE         12.5

As it stands, you could define this table with:

create table DatabaseProducts
 ( Company  varchar(20)
 , Product  varchar(20)
 , Release  varchar(10)
 , constraint DatabaseProductPK
        primary key (Company, Product)
 )

If you wanted the table to contain both Microsoft SQL Server 7.0 and Microsoft SQL Server 2000, then the primary key would have to include the Release column as well.

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