Thanks, @stefano.menci. The date column in the table is using Anvil’s date type, which according to the docs uses Python’s datetime.date. That being the case, as long as I only ever have one entry per day (which I will) then I assume I can use your code above without adding any extra columns.
Just out interest though, can data tables automatically increment a number column, and enforce unique values, to make a reliable primary key column?