Re: What makes difference by creating an index or add a primary key to a table

Daniel:

     I have searched such subject on the web. Many concluded the same thing as you mentioned, but not much about the performance comparsion. According to the closest conclusion, does that mean I only need to create an index ( or indexes) for speedy performance and I can ignore to create the primary key constraint provided that I do not care about the null value of the primary key. Besides, there is never be NULL to both column in my case, so whether or not the parimary key by two columns does not matter. I did found a response that claimed to be faster with the primary key verse the index (very similar case as my, but it is on SQL server). That's what I consern.

Daniel Morgan wrote:

> cschang wrote:
>
> > System: 8.1.7
> > Platform: NT 4 w/sp6a
> > I have a table that I decided to add a primary key by combining two
> > columns. But what that difference to create an index of the table by
> > using these two columns?
> >
> > C Chang
>
> The two objects serve entirely different purposes. The purpose of a
> constraint is to enforce data integrity. The only purpose of an index is
> to enhance performance.
>
> If one looks more specifically at the differences between a primary key
> constraint and a unique constraint (reasonably similar to a unique index)
> there are still differences. Most obviously ... a table can have only a
> single primary key but many unique constraints ... and a unique
> constraint allows NULLs whereas you can not have a NULL primary key.
>
> --
> Daniel Morgan
> http://www.outreach.washington.edu/extinfo/certprog/oad/oad_crs.asp
> damorgan_at_x.washington.edu
> (replace 'x' with a 'u' to reply)
Received on Sun Aug 10 2003 - 21:58:39 CDT