What are the characteristics of a trigger?

Features of triggers: 1. Automatic execution; the trigger is activated immediately after any modification is made to the data in the table. 2. Cascading updates; triggers can make cascading changes through related tables in the database. 3. Strengthen constraints. 4. Track changes. 5. Enforce business logic; triggers can be used to perform administrative tasks and enforce complex business rules that affect the database.

Trigger is a method provided by SQL server to programmers and data analysts to ensure data integrity. It is related to table events. A special stored procedure whose execution is not called by a program or started manually, but is triggered by events. For example, when a table is operated (insert, delete, update), its execution is activated.

Triggers are often used to strengthen data integrity constraints and business rules. Triggers can be found in the DBA_TRIGGERS and USER_TRIGGERS data dictionaries. A SQL3 trigger is a statement that can be automatically executed by the system to modify the database.

Triggers can query other tables and can contain complex SQL statements. They are primarily used to enforce compliance with complex business rules or requirements. For example: You can control whether new orders are allowed to be inserted based on the customer's current account status.

Triggers can also be used to enforce referential integrity so that when rows are added, updated, or deleted in multiple tables, the relationships defined between those tables are preserved. However, the best way to enforce referential integrity is to define primary key and foreign key constraints in the related tables. If you use a database diagram, you can create relationships between tables to automatically create foreign key constraints.

Features of triggers

1. Automatic execution. Triggers are activated immediately after any modification to the table's data (such as manual entry or application operation).

2. Cascade update. Triggers can cascade changes through related tables in the database, which is safer and more reasonable than writing code directly in the foreground.

3. Strengthen constraints. Triggers can reference columns in other tables and can implement more complex constraints than CHECK constraints.

4. Track changes. Triggers can prevent specified updates and changes in the database without permission.

5. Mandatory business logic. Triggers can be used to perform administrative tasks and enforce complex business rules that affect the database.

The role of triggers

can force the data to be verified or converted before writing to the data table.

When an error occurs in the trigger, the result of the change will be undone.

Some database management systems can use triggers for data definition language (DDL), called DDL triggers.

The change command (INSTEAD OF) can be replaced according to specific situations.

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