Can I have an UpDate query to delete all content of all fields in
tblHorses
tblOwners
tblInvoices
You probably need three queries, one for each table. They can be run in
sequence from a Macro or from VBA code.
If you have cascading deletes set up on the relationships between your table -
e.g. tblHorses is related one to many to tblOwners, with the Cascade Deletes
checkbox set, and similarly for tblInvoices - then deleting a record from
tblOwners will delete all the records for that owner from the other two
tables. It won't "delete the content of the fields" - it will remove the
entire record leaving no trace that it was there.
(Be sure you have a backup!!!!! Deletion is a one-way street!)