Generic single-database configuration.

The db connnection strings for the envs are defined in ../alembic.ini (look for key sqlalchemy.url)

Pre-requisites:
export ALEMBIC_USER=<db user>
export ALEMBIC_PASSWORD=<db password>
export PYTHONPATH=<path to /qe/oml/oml>

If these are not provided, code will complain, eg exception like KeyError: 'ALEMBIC_USER'

To upgrade:
alembic  -x db=<env> upgrade <schema version>

eg
alembic  -x db=development upgrade head
alembic  -x db=staging upgrade abc123


To downgrade:
alembic  -x db=<env> upgrade <schema version>

eg
alembic  -x db=staging downgrade abc123
alembic  -x db=development downgrade base (this drops all tables)

To see schema change history:
alembic history

