[butlerm]

Typically you look for orphan rows - the sort of thing ON DELETE CASCADE was invented to prevent. Another thing to check for are records that need to exist but should have references cleared when something else is deleted, e.g. ON DELETE SET NULL. And the third thing is ON DELETE RESTRICT.

You can check for the first two of those things after the fact, and they are relatively benign. In many cases it will make no difference to application queries, especially with the judicious use of outer joins, which should be used for all optional relationships anyway.

If you need ON DELETE RESTRICT application code should probably check anyway, because otherwise you have unexpected delete failures with no application level visibility as to what went wrong. That can be tested for, and pretty much has to be before code that deletes rows subject to delete restrictions is released into production.

As far as race conditions go, they should be eliminated through the use of database transactions. Another alternative is never to delete rows that are referred to elsewhere and just set a deleted flag or something. That is mildly annoying to check for however. Clearing an active flag is simpler because you usually want rows like that to stay around anyway, just not be used in new transactions.