Class::DBI lets you do a simple "eq" test for sameness of database objects.

It uses overload to return an encoded key value in a string context, so that $a eq $b works anywhere that primary keys have been declared and both are from the same table.

Update: This overloading leads to a trivial Schwartzian Transform: @t = map { [$_, "$_"] } @u, potentially making any sorting or duplicate checking lightening fast!!