Multiple Columns Index/Key (does it free me from creating a single column indexes?)

I hope i'm in the right place, but thanks anyway....

Actually i have 2 questions (regarding sql-server Indices/Keys):

1) I have an index, which is consisted of 4 columns.

I've read elsewhere that this index functions (as well) as an index (single column

index) on the first column of this multi-column index.

Does this mean that if i'd like to have (in addition) Indices on all of the 4 columns

seperately i need to define only 3?

2) I have a unique key consisted of multiple columns.

I'd like to save an index to this combination of columns as well (to speed up

things in DB...).

Does the definition of a multiple-columns key free me from defining the multiple-

columns index?

can anyone explain the main diference between Keys and Indices?

1. I'm sure you are in the wrong place, try the SQL Server forums.

2. A Key implies unique data in the column(s) (Unique Key / Primary Key) where as an index doesn't necessarily have to have unique data in the column(s).

3. An index and a key that use the same definitions (same columns etc.) would be redundant, cost space (and possibly performance) and not desired. The optimizer can use either.

4. The first column of an index is always the most important and determines whether the index will be used or not. If you have no better indexes of the first column then it will be used.

BTW - Don't over do it with indexes!

Please ask such question in the SQL Server Forum, this forum is only for Team Edition for Database Professionals.

Alle