code: func UpdateDeleteRange(ctx sessionctx.Context, dr DelRangeTask, newStartKey, oldStartKey kv.Key) error {
  	newStartKeyHex := hex.EncodeToString(newStartKey)
  	oldStartKeyHex := hex.EncodeToString(oldStartKey)
  	sql := fmt.Sprintf(updateDeleteRangeSQL, newStartKeyHex, dr.JobID, dr.ElementID, oldStartKeyHex)
  	_, err := ctx.(sqlexec.SQLExecutor).Execute(context.TODO(), sql)
  	return errors.Trace(err)
  }
docs: // UpdateDeleteRange is only for emulator.