[techno_kid]

what is the difference between primary key and unique key?

thanks a lot.. =)

[snif innards]

a primary key has to be a unique key but, a unique key dosen't have to be a primary key

[techno_kid]

oh i see =)
but is it only the difference? i mean, what are their specific purposes?
primary key is primarily for what?
and unique key is basically for what?

im a newbie in database programming.. =)
thanks snif...
i appreciate your help.. =)

[Chankama]

Well.. A primary key is something that is used for indexing the rows of a database. Naturally, it has to be unique. But, I guess you could have unique keys that are not necessarily primary keys. The uniqueness of the column could be a constraint of the database for example.

A person Social Insurance Number and Drivers License Number can be two unique keys that "must" be enforced at all times. But, only one of them needs to be selected as a primary key. If you don't want to, then you can introduce a surrogate key that is auto-generated by the databse system everytime you create a new row.

[techno_kid]

thanks chankama..
that's a great help... =)