Mysql 简明教程
MySQL - DROP TRIGGER
MySQL 中的触发器类似于过程，是一些存储程序。它们可以在与事件关联的表、架构、视图和数据库上创建，并且每当事件发生时便会调用相应的触发器。
Triggers in MySQL are stored programs similar to procedures. These can be created on a table, schema, view and database that are associated with an event and whenever an event occurs the respective trigger is invoked.
在实际上，触发器编写为对以下任一事件响应而执行：
Triggers are, in fact, written to be executed in response to any of the following events −
-
A database manipulation (DML) statement (DELETE, INSERT, or UPDATE)
-
A database definition (DDL) statement (CREATE, ALTER, or DROP).
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A database operation (SERVERERROR, LOGON, LOGOFF, STARTUP, or SHUTDOWN).
您可以使用 DROP TRIGGER 语句删除触发器。
You can delete a trigger using the DROP TRIGGER Statement.
Dropping Trigger in MySQL
MySQL 中的 DROP TRIGGER 语句将从数据库中删除触发器及其所有信息。
The DROP TRIGGER statement in MySQL will drop a trigger from a database, and all its information.
Syntax
以下是 MySQL DROP TRIGGER 语句的语法。
Following is the syntax of the MySQL DELETE TRIGGER Statement.
DROP TRIGGER [IF EXISTS] trigger_name其中，trigger_name 是您需要删除的触发器的名称。
Where, trigger_name is the name of the trigger you need to delete.
Example
假设我们创建了一个名为 student 的表，如下所示：
Assume we have created a table with name student as shown below −
CREATE TABLE STUDENT(
Name varchar(35),
Age INT,
Score INT
);以下查询在此表上创建了一个名为 sample_trigger 的触发器。如果您输入的值小于 0，则此触发器会将分数值设置为 0 分。
Following query creates a trigger named sample_trigger on this table. This trigger will set the score value 0 if you enter a value that is less than 0 as score.
DELIMITER //
CREATE TRIGGER sample_trigger
BEFORE INSERT ON STUDENT
FOR EACH ROW
BEGIN
IF NEW.score < 0 THEN SET NEW.score = 0;
END IF;
END //
DELIMITER ;现在，让我们使用以下查询来删除我们在上一步中创建的触发器：
Now, let us use the following query to drop the trigger we created in the previous step −
DROP TRIGGER sample_trigger;With IF EXISTS clause
如果您尝试删除不存在的触发器，将会生成如下所示的错误：
If you try to drop a trigger that doesn’t exist an error will be generated as shown below −
DROP TRIGGER demo;输出如下：
Following is the output −
ERROR 1360 (HY000): Trigger does not exist如果您按照下面所示，将 IF EXISTS 子句与 DROP TRIGEGR 语句一起使用，则将删除指定的触发器；如果具有给定名称的触发器不存在，则将忽略此查询。
If you use the IF EXISTS clause along with the DROP TRIGEGR statement as shown below, the specified trigger will be dropped and if a trigger with the given name, doesn’t exist the query will be ignored.
DROP TRIGGER IF EXISTS demo;