It sounds like you are importing these records from Excel. If you set strict validation on the match field in FMP into which the some-times valid column is imported, only the valid records will import. FMP will stop invalid records from importing if the FMP field definition requires the valid data.
This does mean you will have to be very specific about what is valid data when modifying the field definition's validation rule(s).
Thanks for the help Stephen. I tried your suggestion and got most of it by creating a list of the acceptable field items. When I ran that, I still got a couple of blank records, so I modified the import script to require that each cell of that field be non-empty and equal to one of the items on the list of acceptable field items. Still getting rows of empty records?? Any ideas?
Another way to do this:
Import the excel file into a temporary table, then use a script to process these records. It would afford you more control over what data is allowed into your solution.
You could run a clean-up script after the import, constraining the imported records (the found set at the end of the import) to records which have unwanted blanks, and then deleting that resulting found set.
The only drawback is that you no longer have your imported records as the active found set. In fact, at the end of that Delete Found Set, you have no records in the found set until you either Show All or perform a new Find.