RE: Can composite indexes be used as an index on a single field?

SSC Guru

Points: 323506

April 3, 2014 at 11:45 am

since you said the PartNumber is the first field, then yes; but it also depends on how selective that single column is.

if there's a lot of common values, SQL might just decide to do a clustered index scan instead.

so to confirm, if PartNumber is the leading column in your index that has three fields, would it be posible for a query to use the index.

so if the index is (PartNumber,SecondKey,ThirdKey) then yes.

if the index was created as (FirstKey,SecondKey,PartNumber) then no, you'd need an extra idnex.

Lowell

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