|A table that tracks time periods may require period uniqueness. That means it has no sequenced duplicates.|
If a table has columns processID, start_date and end_date, those three columns are period unique if there exists no pair of rows with the same processID and overlapping start_date and end_date values. If there is such a pair of rows, the table exhibits sequenced duplication.
Another way of saying it: if an instant is the smallest datetime unit of start_date and end_date columns, then if there are no sequenced duplicates, there is exactly one processID value at any instant.
Here is a query to find sequenced duplicates for those columns: