Posted by jerry gitomer on 07/21/05 16:03

Gordon Burditt wrote:
>>I don't really understand the difference between primary key and
>>unique. Should I use primary key instead of unique?
>
>
> A primary key is, essentially, the first unique index. The distinction
> is mostly for the programmer and automatic tools that diagram
> relationships between tables.
Gordon L. Burditt

Be aware that this is RDBMS dependent as in some vendors
databases NULL is not a permitted value in the primary key
index, but is permitted in the unique key index.

HTH
Jerry

[Back to original message]