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What this article shares with you is about the use of triggers in the database. The editor thinks it is very practical, so I share it with you to learn. I hope you can get something after reading this article. Let's take a look at it.

The syntax for creating a database trigger is: [CREATE

In MySQL 5.7, you can use CREATE TRIGGER statements to create triggers.

The syntax format is as follows:

CREATE

ON FOR EACH Row

The syntax is as follows:

1. Trigger name

The name of the trigger, which must have a unique name in the current database. If you want to create it in a particular database, the name should be preceded by the name of the database.

2. INSERT | UPDATE | DELETE

A trigger event that specifies the type of statement that activates the trigger.

3. BEFORE | AFTER

BEFORE and AFTER, when the trigger is triggered, indicates that the trigger is fired before or after the statement that activates it. Use the BEFORE option if you want to verify that the new data meets the criteria; if you want to make several or more changes after the statement that activates the trigger is executed, you usually use the AFTER option.

4. Table name

The table name associated with the trigger, which must be a permanent table and cannot be associated with a temporary table or view. The trigger is activated only when an event is triggered on the table.

The same table cannot have two triggers with the same trigger time and event. For example, for a data table, you cannot have two BEFORE UPDATE triggers at the same time, but you can have one BEFORE UPDATE trigger and one BEFORE INSERT trigger, or one BEFORE UPDATE trigger and one AFTER UPDATE trigger.

5. Trigger body

The trigger action body, which contains the MySQL statement that will be executed when the trigger is activated. If you want to execute multiple statements, you can use BEGIN... END compound statement structure.

6 、 FOR EACH ROW

It generally refers to the row-level trigger, and the action of the trigger is activated for each row affected by the trigger event. For example, when you insert multiple rows of data into a table using an INSERT statement, the trigger performs the corresponding trigger action for each row of data insertion.

The above is the use of triggers in the database, the editor believes that there are some knowledge points that we may see or use in our daily work. I hope you can learn more from this article. For more details, please follow the industry information channel.

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