MySQL允许在C中的回调，以便当发生更改时，我可以通知？ [英] Does MySQL permit callbacks in C such that when a change happens, I can be notified?

问题描述

MySQL允许C中的回调，以便在数据库中发生更改（如插入）时，由不同的程序或用户在命令行执行，我可以通知？

Does MySQL permit callbacks in C such that when a change happens in the database, like an insert, that is performed by a different program or by the user at the command line, I can be notified?

我猜想它没有，因为mysqlclient是一个库，不是一个正在运行的线程。

I am guessing that it doesn't, because mysqlclient is a library, not a running thread. But I may as well ask.

推荐答案

创建一个这样的触发器。

Create a trigger like so.

DELIMITER $$

CREATE TRIGGER ad_mytable_each AFTER DELETE ON MyTable FOR EACH ROW
BEGIN
  #write code that trigger After delete (hence the "ad_" prefix)
  #For table MyTable (The _MyTable_ middle)
  #On each row that gets inserted (_each suffix)
  #
  #You can see the old delete values by accesing the "old" virtual table.
  INSERT INTO log VALUES (old.id, 'MyTable', old.field1, old.field2, now());

END$$

DELIMITER ;

有 INSERT ， DELETE ， UPDATE

他们可以触发 BEFORE 或 AFTER 后的操作。

触发器 BEFORE

There are triggers for INSERT, DELETE, UPDATE
And they can fire BEFORE or AFTER the action.
The trigger BEFORE the action can cancel the action by forcing an error, like so.

CREATE TRIGGER bd_mytable_each BEFORE DELETE ON MyTable FOR EACH ROW
BEGIN
  #write code that trigger Before delete (hence the "db_" prefix)
  declare DoError Boolean; 

  SET DoError = 0;

  IF old.id = 1 THEN SET DoError = 1; END IF; 

  IF (DoError = 1) THEN SELECT * FROM Table_that_does_not_exist_to_force_error;
  #seriously this example is in the manual.

END$$

DELIMITER ;

这将防止删除记录1.

This will prevent deletion of record 1.

A before UPDATE触发器甚至可以更改更新的值。

A before UPDATE Trigger can even change the values updated.

CREATE TRIGGER bu_mytable_each BEFORE UPDATE ON MyTable FOR EACH ROW
BEGIN
  IF new.text = 'Doon sucks' THEN SET new.text = 'Doon rules';
END$$

DELIMITER ;

希望你会成为Trigger的快乐。

Hope you'll be Trigger happy.

这篇关于MySQL允许在C中的回调，以便当发生更改时，我可以通知？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！