apache derby triggers

In Apache Derby, a trigger is a named database object that is associated with a table and is automatically executed in response to certain events, such as a row being inserted, updated, or deleted. Triggers can be used to enforce business rules, perform complex calculations, and maintain data integrity.

Here is the basic syntax for creating a trigger in Apache Derby:

CREATE TRIGGER trigger_name
BEFORE/AFTER INSERT/UPDATE/DELETE ON table_name
FOR EACH ROW [MODE DB2SQL] [ENABLE/DISABLE]
trigger_body

In this syntax, trigger_name is the name of the trigger, table_name is the name of the table that the trigger is associated with, and trigger_body is the code that is executed when the trigger is fired. The BEFORE/AFTER keyword specifies whether the trigger is executed before or after the event occurs, and the INSERT/UPDATE/DELETE keyword specifies the type of event that the trigger is associated with. The FOR EACH ROW clause specifies that the trigger is executed once for each row that is affected by the event. The MODE DB2SQL clause specifies that the trigger uses DB2 SQL syntax, and the ENABLE/DISABLE clause specifies whether the trigger is enabled or disabled.

Here is an example of creating a trigger in Apache Derby:

CREATE TRIGGER update_salary
AFTER UPDATE OF salary ON employees
REFERENCING NEW AS new_row
FOR EACH ROW
UPDATE salary_history SET salary = new_row.salary
WHERE employee_id = new_row.employee_id;

In this example, a trigger named update_salary is created that is executed after an UPDATE statement is executed on the salary column of the employees table. The REFERENCING NEW AS new_row clause specifies that the new_row variable contains the new values for the updated row. The FOR EACH ROW clause specifies that the trigger is executed once for each row that is updated. The trigger body updates the salary_history table with the new salary value for the employee.

Triggers can be a powerful tool for enforcing business rules and maintaining data integrity in Apache Derby. However, it's important to carefully design and test your triggers to ensure that they function correctly and efficiently. Triggers can also have a significant impact on database performance, so it's important to monitor their performance and optimize them as necessary.