MySQL Learning Note (12) trigger (trigger)

Trigger (Trigger)

1. Role: Monitor a situation and trigger an action.

The trigger can monitor the increase, deletion and change of the table, and make the operation of adding, deleting and changing.

2. Create TRIGGER Syntax: (Requires early modification of Terminator: delimiter Terminator)

CREATE TRIGGER trigger_name

After/before

increase, delete, change on Table name

F or each ROM

B Egin SQL statements;

E nd End Character

Trigger Name

Trigger Time

A the difference between fter and before:

A fter: complete the data operation before triggering.

B Efore: Actions that trigger the data before the operation is monitored

Events monitored by triggers

Trigger Watch Locations

Events triggered by triggers

3. the value of the trigger reference row:

1. for inset, the newly added line is represented by new.

the values for each row in the line are new. Column name  

2. For delete, there was a row, then deleted, to refer to the deleted row, with Old . Column name

3. for update, the modified row is modified by using the old. Column name

When modified, use the new column name

4. To delete a trigger:

D ROP Trigger trigger name

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MySQL Learning Note (12) trigger (trigger)