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The characteristics of the trigger: 1, automatic execution; the trigger is activated immediately after making any changes to the data of the table. 2. Cascading updates; triggers can cascade changes through related tables in the database. 3. Strengthen the constraint. 4. Track the changes. 5. Enforce business logic; triggers can be used to perform administrative tasks and force complex business rules that affect the database.

Trigger is a method that SQL server provides to programmers and data analysts to ensure data integrity. It is a special stored procedure related to table events. Its execution is not called by the program, nor started manually, but triggered by events. For example, when an operation is performed on a table (insert,delete, update), it is activated.

Triggers are often used to strengthen data integrity constraints and business rules. Triggers can be found in the DBA_TRIGGERS, USER_TRIGGERS data dictionary. The trigger of SQL3 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 mainly 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 the relationships defined between tables are retained when rows are added, updated, or deleted in multiple tables. However, the best way to enforce referential integrity is to define primary and foreign key constraints in related tables. If you use a database diagram, you can create relationships between tables to automatically create foreign key constraints.

Characteristics of flip-flop

1. Automatic execution. Triggers are activated immediately after making any changes to the table's data, such as manual input or application operations.

2. Cascading updates. Triggers can make cascading changes through related tables in the database, which is more secure and reasonable than writing code directly in the foreground.

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

4. Track the changes. Triggers prevent unauthorized specified updates and changes in the database.

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

The function of trigger

Data can be forcibly verified or converted before being written to the data table.

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

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

The abnormal instruction (INSTEAD OF) can be replaced according to the specific situation.

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