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This article mainly introduces the role of database triggers, the article is very detailed, has a certain reference value, interested friends must read it!

The role of triggers in the database: triggers are mainly used to enforce complex business rules and requirements, but also help to enforce the integrity of references to preserve defined relationships between tables when adding, updating, or deleting rows in a table.

Trigger

A trigger is a special type of stored procedure that takes effect when data is modified in a specified table using one or more of the following data modification operations: UPDATE, INSERT, or DELETE. Triggers can query other tables and can contain complex SQL statements. They are mainly used to enforce complex business rules or requirements. For example, you can control whether orders are allowed to be inserted based on the customer's current account status.

Triggers also help enforce referential integrity to preserve defined relationships between tables when rows in a table are added, updated, or deleted. 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.

Advantages of using triggers

(1) triggers are automatic: they are activated immediately after making any changes to the data in the table (such as manual input or actions taken by the application).

(2) triggers can make cascading changes through related tables in the database. For example, you can write a delete trigger on the title_id column of a titles table to cause matching rows in other tables to take a delete operation. The trigger uses the title_id column as the unique key to locate the matching rows in the titleauthor, sales, and roysched tables.

(3) triggers can enforce restrictions that are more complex than those defined with CHECK constraints. Unlike CHECK constraints, triggers can reference columns in other tables. For example, a trigger can roll back an attempt to apply a discount to a book that costs less than $10 (stored in the titles table)

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