The role of triggers in the database: Triggers are mainly used to enforce complex business rules and requirements. They also help to enforce referential integrity to facilitate retention when adding, updating, or deleting rows in the table. Defined relationships between tables.
Trigger
A trigger is a special type of stored procedure that when using one of the following or Triggers will take effect when multiple data modification operations modify data in the specified table: 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 order insertion is allowed based on the customer's current account status.
Triggers also help enforce referential integrity so that defined relationships between tables are preserved when rows in the table are added, updated, or deleted. 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.
Advantages of using triggers
(1) Triggers are automatic: they are automatically used when any modifications are made to the data in the table (such as manual input or application actions). is activated immediately after the operation).
(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 the titles table to cause a delete action for each matching row in the other table. This trigger uses the title_id column as the unique key to locate 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 could rollback an attempt to apply a discount on books priced under $10 (stored in the titles table)
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