SQl Server indexing, same column 2 different indexes?

I have 2 queries I need to run against my DB. One loo开发者_Go百科ks for ManufacturerID and the other looks for ManufacturerID and SalesRepID.

Should I have 1 index on ManufacturerID and 1 index on SalesRepID

OR

1 Index on ManufacturerID and 1 Index on ManufacturerID and SalesRepID?

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It depends. If your table is big enough, and your data is sparse enough, it might make sense to have:

1. Index on ManufacturerID
2. Index on ManufacturerID, SalesRepID

On the other hand, if you have just a few different SalesRepID for each ManufacturerID, then both queries will be probably very well optimized just by using index on ManufacturerID.

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Normally, you'd only need one index on both one index on ManufacturerID and SalesRepID.

A search on ManufacturerID should still use this composite index as long it is the left hand column on the index key columns.