Re: Indexing Question.

In article <3h0uec$lb_at_charnel.ecst.CSUChico.EDU>, tvangod_at_ecst.csuchico.edu (Tyler Van Gorder) says:

>If you have a 4 part primary key do you need to define an index on each
>column or can you define an index on the entire key. If the second is
>the case, how is performance when say 2 of the 4 columns are supplied in
>a query?

Yes, you can build an index on the entire key. When you supply only part of the key in a query, the index will be used if and only if the values you supply are a leading portion of the key. That is, given an index on columns A, B, C, and D for table Q:

These queries will use the index

	SELECT column_list
	FROM   Q
	WHERE  A = 'hi';


	SELECT column_list
	FROM   Q
	WHERE  A = 'hi'
	AND    B = 'there'
	AND    C = 'Tyler';

While this query will not:

	SELECT column_list
	FROM   Q
	WHERE  A = 'hi'
	AND    C = 'Tyler'

Hope this helps.

Keith Thompson *<:o) Received on Thu Feb 09 1995 - 03:42:52 CET