/usr/share/doc/dbconfig-common/examples/db-test-mysql-2.1/mysql-upgrade_2.1.sql is in dbconfig-common 1.8.47+nmu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | -- this sql should automatically be sourced for upgrades from pre-2.1 versions
update mytable set version='2.1';
|