Re: If an index is based on 3 columns will a query using two of the columns utilize the index?

On Mon, Sep 12, 2005 at 09:43:57AM -0400, Reid Thompson wrote:
> Example:
> assume a table of 10 columns, three of which are fname, lname, and dob.
> If an index is created on (fname, lname, dob), will a query that
> utilizes two of the columns ( select 'data' from table where fname = 'X'
> and lname = 'Y') utilize the index?

Yes, if it is selective enough.  (It _can_ use the index, which does not
mean that it _will_ use it.)  Note that if your example query used the
columns (lname, dob), the answer would be "no."

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Alvaro Herrera -- Valdivia, Chile         Architect, www.EnterpriseDB.com
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