code: func checkAndInitDBPriv(ctx sessionctx.Context, dbName string, is infoschema.InfoSchema, user string, host string) error {
  	ok, err := dbUserExists(ctx, user, host, dbName)
  	if err != nil {
  		return err
  	}
  	if ok {
  		return nil
  	}
  	// Entry does not exist for user-host-db. Insert a new entry.
  	return initDBPrivEntry(ctx, user, host, dbName)
  }
docs: // checkAndInitDBPriv checks if DB scope privilege entry exists in mysql.DB.
  // If unexists, insert a new one.