Index scan question

[Don Coleman]

List:

After several tests I would like opinions on the following observations:

Built an index on a YESNO field where for a *report export process where 
I only want to select 11 (YESNO) eq "" (blank)

There are 465,000 records in this file.   This export is to run every 3
minutes so I would expect a maximum of 2000-3000 records (peak periods) to
be selected for each 3 minute interval scan.  The number exported could drop
to several hundred records or less during non-peak times.  However when I
run the *report export process the app. still reads through 25,000-30,000
records.  While that's not the entire file and some time has been saved, I
don't understand why it is not only reading the exact records to be
selected.  There is no select process involved and no "ne" statement in my
selection set.  The selection set is simply:

Group	Field		Description		REL	Value
	11		Exported (Y/N)	eq

In an attempt to give the indexed records some "uniqueness" I also tried
adding a time stamp field as the second field in the index.  That appeared
to have no effect on the number of records selected.  After a record is
exported field 11 has a "Y" written to it so it is only exported once.

Don Coleman
Donald G. Coleman, Consultant
402 Andrew Circle
Indiana, PA 15701
dcoleman at dgcreact.com
(724) 349-6302