You may hit this error while populating database for any of the service for OpenStack.  Below is the error output thrown while populating database for neutron service on OpenStack (Juno). 
root@stack:~#  /bin/sh -c "neutron-db-manage --config-file /etc/neutron/neutron.conf \
>   --config-file /etc/neutron/plugins/ml2/ml2_conf.ini upgrade juno" neutron
INFO  [alembic.migration] Context impl SQLiteImpl.
INFO  [alembic.migration] Will assume non-transactional DDL.
INFO  [alembic.migration] Running upgrade None -> havana, havana_initial
INFO  [alembic.migration] Running upgrade havana -> e197124d4b9, add unique constraint to members
Traceback (most recent call last):
  File "/usr/bin/neutron-db-manage", line 10, in 
    sys.exit(main())
  File "/usr/lib/python2.7/dist-packages/neutron/db/migration/cli.py", line 173, in main
    CONF.command.func(config, CONF.command.name)
  File "/usr/lib/python2.7/dist-packages/neutron/db/migration/cli.py", line 83, in do_upgrade_downgrade
    do_alembic_command(config, cmd, revision, sql=CONF.command.sql)
  File "/usr/lib/python2.7/dist-packages/neutron/db/migration/cli.py", line 61, in do_alembic_command
    getattr(alembic_command, cmd)(config, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/alembic/command.py", line 125, in upgrade
    script.run_env()
  File "/usr/lib/python2.7/dist-packages/alembic/script.py", line 203, in run_env
    util.load_python_file(self.dir, 'env.py')
  File "/usr/lib/python2.7/dist-packages/alembic/util.py", line 212, in load_python_file
    module = load_module_py(module_id, path)
  File "/usr/lib/python2.7/dist-packages/alembic/compat.py", line 58, in load_module_py
    mod = imp.load_source(module_id, path, fp)
  File "/usr/lib/python2.7/dist-packages/neutron/db/migration/alembic_migrations/env.py", line 108, in 
    run_migrations_online()
  File "/usr/lib/python2.7/dist-packages/neutron/db/migration/alembic_migrations/env.py", line 100, in run_migrations_online
    context.run_migrations()
  File "", line 7, in run_migrations
  File "/usr/lib/python2.7/dist-packages/alembic/environment.py", line 688, in run_migrations
    self.get_context().run_migrations(**kw)
  File "/usr/lib/python2.7/dist-packages/alembic/migration.py", line 258, in run_migrations
    change(**kw)
  File "/usr/lib/python2.7/dist-packages/neutron/db/migration/alembic_migrations/versions/e197124d4b9_add_unique_constrain.py", line 42, in upgrade
    local_cols=['pool_id', 'address', 'protocol_port']
  File "", line 7, in create_unique_constraint
  File "/usr/lib/python2.7/dist-packages/alembic/operations.py", line 621, in create_unique_constraint
    schema=schema, **kw)
  File "/usr/lib/python2.7/dist-packages/alembic/ddl/sqlite.py", line 21, in add_constraint
    "No support for ALTER of constraints in SQLite dialect")
NotImplementedError: No support for ALTER of constraints in SQLite dialect
This error is because config file has two database connections, one is for MySQL and  other is for Sqlite, since i'm using mysql and i forgot to comment Sqlite, i  hit this error.

All you need to do to fix this is comment/remove sqlite connection from /etc/neutron/neutron.conf and then populate it.

gil ...