Triggers in Oracle are stored procedures used to automatically perform operations after a specific event (insert, update, or delete). They are used in a variety of scenarios, including data verification, auditing, and data maintenance. When creating a trigger, you need to specify the trigger name, association table, trigger event, and trigger time. There are two types of triggers: the BEFORE trigger is fired before the operation, and the AFTER trigger is fired after the operation. For example, the BEFORE INSERT trigger ensures that the age column of the inserted row is not negative.
Guide to using triggers in Oracle
A trigger is a special type of stored procedure stored in a database that is automatically executed when its associated event (insert, update, or delete) is triggered. They are used to perform specific actions in data operations, such as enforcing business rules, conducting audits, or maintaining data integrity.
Create a trigger
To create a trigger, you can use the following syntax:
<code>CREATE TRIGGER [trigger_name] ON [table_name] FOR [trigger_event] [trigger_timing] AS BEGIN -- 觸發(fā)器代碼END;</code>
trigger_name: The unique name of the trigger.
table_name: The table name associated with the trigger.
trigger_event: Events that trigger triggers, such as INSERT, UPDATE, or DELETE.
trigger_timing: The time when the trigger is triggered, such as BEFORE or AFTER.
Trigger type
There are two types of triggers:
- BEFORE Trigger: Triggered before the operation is executed.
- AFTER Trigger: Triggered after the operation is executed.
Trigger example
Create a BEFORE INSERT trigger to ensure that the "age" column of the inserted row is not negative:
<code>CREATE TRIGGER check_age_insert ON employees BEFORE INSERT AS BEGIN IF NEW.age </code>
Trigger usage
Triggers are useful in the following scenarios:
- Data Verification: Ensure the data complies with business rules.
- Audit: Record operations on data.
- Data maintenance: Automatically perform maintenance tasks when performing data operations, such as updating reference tables.
- Cascading update: Automatically propagate changes to the parent table to the child table.
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