If you have two SQLite databases which are the same tables, you can merge them by attaching and then inserting.
$ sqlite3 data.sqlite3 SQLite version 3.31.1 2020-01-27 19:55:54 Enter ".help" for usage hints. sqlite> attach 'data2.sqlite3' as merge; sqlite> .table archive merge.archive sqlite> begin; sqlite> insert into archive select * from merge.archive; sqlite> commit; sqlite> detach merge; sqlite> .quit
It is also just a useful way to handle multiple databases in a single session.