what is a trigger

Trigger "Trigger" is a special object in the database management system. It is associated with a table and is used to automatically trigger a series of operations or logic when a specific event occurs on the table. It is usually used to implement Data integrity constraints, audit logs, data change records and other requirements, when the conditions defined by the trigger are met, the trigger will be triggered to perform the corresponding action.

# Operating system for this tutorial: Windows 10 system, Dell G3 computer.

A trigger is a special object in a database management system that is associated with a table and used to automatically trigger a series of operations or logic when specific events on the table occur.

Triggers are usually used to implement requirements such as data integrity constraints, audit logs, and data change records. When the conditions defined by the trigger are met, the trigger will be triggered to perform the corresponding action.

Triggers can be triggered on the following events:

1. INSERT: Triggered when a new row is inserted into the table.
2. UPDATE: Triggered when a row in the table is updated.
3. DELETE: Fires when a row is deleted from the table.

When the above events occur, triggers can perform a variety of operations, such as:

1. Data validation and integrity checks: Triggers can check for inserts, updates, or deletes Whether the operation complies with the defined rules and constraints, such as primary key constraints, foreign key constraints or unique constraints, etc.
2. Logging and auditing: Triggers can be used to record detailed information about data changes for auditing and tracking operation history.
3. Data derivation and calculation: Triggers can automatically update other related columns based on changes in certain columns, or perform complex data calculation logic.
4. Trigger other business logic and stored procedures: Triggers can call other stored procedures or business logic to perform some additional operations.

Triggers are defined and managed in the database management system. The specific syntax and usage may vary depending on different database systems. Typically, triggers use a specific trigger definition language (Trigger Definition Language) to define their conditions and actions.

It should be noted that when designing and using triggers, overly complex and frequent triggers should be avoided to avoid affecting database performance and maintainability.

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