A query: anyone know what's up with indexes on date fields?

Hi. I'm trying to speed up performance of a forms query where substr(database-date-field,1,9) = <value-of-forms-date-field>

So I created an index on the database-date-field. Trouble is it doesn't seem to help any. I think the problem *may* be that I'm using the substr in the where clause - it doesn't seem to use the index when you use substr (??? not sure ???). And of course, it won't let you create an index on a substr'd field (dammit).

*And* of course, the only way to query by date and get any results is to use the substr. Since date/time values are intrinsically unique, how the hell am I supposed to pull records with common dates (ignoring the time portion) utilizing an index so I don't fall asleep in the process???? (It's a huge file, by the way....).

Any ideas?

Thanks.....john

-- 
    ---{john hayes}  OLDOMINISITY; Norfolk, Virginia USA
                     internet: aiko_at_cs.odu.edu