message: Adding column only if it doesn't already exist
diff: @@ -586,10 +586,13 @@ def load_birth_names():
  obj.main_dttm_col = 'ds'
  obj.database = utils.get_or_create_main_db()
  obj.filter_select_enabled = True
  +
  + if not any(col.column_name == 'num_california' for col in obj.columns):
  obj.columns.append(TableColumn(
  column_name='num_california',
  expression="CASE WHEN state = 'CA' THEN num ELSE 0 END"
  ))
  +
  db.session.merge(obj)
  db.session.commit()
  obj.fetch_metadata()
  