code: func (e *RevokeExec) Next(ctx context.Context, req *chunk.RecordBatch) error {
  	if e.done {
  		return nil
  	}
  	e.done = true
  
  	// Revoke for each user.
  	for _, user := range e.Users {
  		// Check if user exists.
  		exists, err := userExists(e.ctx, user.User.Username, user.User.Hostname)
  		if err != nil {
  			return err
  		}
  		if !exists {
  			return errors.Errorf("Unknown user: %s", user.User)
  		}
  
  		err = e.revokeOneUser(user.User.Username, user.User.Hostname)
  		if err != nil {
  			return err
  		}
  	}
  	domain.GetDomain(e.ctx).NotifyUpdatePrivilege(e.ctx)
  	return nil
  }
docs: // Next implements the Executor Next interface.