res = conn.execute('select secret, key, id from client')
results = res.fetchall()
clients = [{'secret': r[0], 'key': r[1], 'is_active': True, 'client_id': r[
    2], 'created_at': datetime.datetime.now(), 'updated_at': datetime.
    datetime.now()} for r in results]
op.bulk_insert(client_credential, clients)
op.drop_column('client', 'secret')
op.drop_column('client', 'key')
Fetch table values using alembic and update to another table.