Validate new records against exisiting records

J

Joe Bohen

I use a database to track fuel use by company employees
when a card is issued to a member of staff the starting
date for this card use is recorded in the start date field
when the member of staff leaves or moves to another
department the end date for the card record is completed.
This is carried out via a form. When the card is re-issued
I need a validation rule to check whether there are any
overlaps in the use period for the new card record. I.e.
if the card 00757 has a closing date of 20/08/03 and card
00757 is reissued with a starting date of 19/08/03 there
could be duplication of records in other tables related to
card use.

Any ideas on how to write the validation rule would be
much appreciated.
 

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