Re: One example of a slow query.

"David Segall" <david@[EMAIL PROTECTED]
> wrote in message 
news:nu2464djgj6vku4tci9if3ics221qidcp5@[EMAIL PROTECTED]
> "David Cressey" <cressey73@[EMAIL PROTECTED]
> wrote:
>
>> Because
>>there was an index with a compound index key,  namely country, state,
and
>>city.
> Why would you do that instead of indexing the fields separately?

Most DBMS engines will use only one index for a particular restriction
step, 
so in general you will want to define compound keys where they make sense.

Depending on the implementation of the index it might be possible to
exploit 
right-incomplete key values, so you would try to define your key with the 
most frequently known parts of the key are on the left.  Then although the

key may include more columns than you can supply a value for, you might 
still be able to exploit it if you supply the parts you do know.

Roy