Create MySQL trigger syntax

MySQL triggers use the create trigger statement. The following describes the statement syntax for creating a MySQL TRIGGER in detail. It is helpful for you to learn about MySQL triggers.

Create trigger create MySQL TRIGGER) syntax
Create trigger trigger_name trigger_time trigger_event
ON tbl_name for each row trigger_stmt
A trigger is a table-related named database object. This object is activated when a specific event occurs on the table.

The trigger program is related to the table named tbl_name. Tbl_name must reference a permanent table. You cannot associate the trigger program with the TEMPORARY table or view.

Trigger_time is the time when the program is triggered. It can be BEFORE or AFTER to indicate that the trigger program is triggered BEFORE or AFTER its statement is activated.

Trigger_event indicates the type of statements used to activate the trigger program. Trigger_event can be one of the following values:
· INSERT: the trigger program is activated when a new row is inserted into the table, for example, through INSERT, load data, and REPLACE statements.
· UPDATE: the trigger program is activated when a row is changed, for example, through the UPDATE statement.
· DELETE: the trigger program is activated when a row is deleted from the table, for example, through the DELETE and REPLACE statements.
Note that trigger_event is not very similar to the SQL statement used to activate the trigger program in the form of table operations, which is very important. For example, the BEFORE trigger program for INSERT can be activated by both the INSERT statement and the load data statement.

One of the examples that may cause confusion is insert .. on duplicate update... syntax: The before insert trigger will be activated for each row, followed by the after insert trigger program, or the before update and after update trigger programs, depending on whether there is a duplicate key on the row.

For a given table with the same triggering program action time and event, there cannot be two triggering programs. For example, a table cannot have two before update triggers. However, there can be one before update trigger program, one before insert trigger program, one before update trigger program, and one after update trigger program.

Trigger_stmt is the statement executed when the trigger program is activated. If you want to execute multiple statements, you can use the in... END compound statement structure. In this way, the same statements allowed in the stored subroutine can be used.

The preceding section describes the syntax for creating a MySQL trigger.

Three examples of mysql triggers

How to Create a master-slave server for mysql

Obtain the MySql time function of the current time

Mysql Aggregate functions

Use of MySQL concat Functions