How to create triggers from oracle

A trigger is a database object that automatically executes SQL statements when a specific event occurs. In Oracle, triggers can be created through the CREATE TRIGGER statement that specifies the trigger name, execution time, action table, trigger events, and SQL statement code. Triggers can be used to perform actions automatically when records are inserted, updated, or deleted. For example, when inserting a new record in the customers table, you can create a trigger to update the last_updated column. Triggers can also use PL/SQL blocks for more complex operations and support a variety of types such as Row, Statement, and System.

How to create triggers using Oracle

A trigger is a database object that automatically executes SQL statements when a specific event occurs. Triggers in Oracle can be used to perform various tasks, such as automatically performing operations when inserting, updating, or deleting records.

Create a trigger

To create a trigger, you can use Oracle's CREATE TRIGGER statement. This statement uses the following syntax:

 <code class="sql">CREATE TRIGGER  BEFORE | AFTER | INSTEAD OF [FOR EACH ROW] ON  FOR  AS </code>

in:

• : The name of the trigger to be created.
• BEFORE | AFTER | INSTEAD OF : Specifies that the trigger executes before, after or in place of the event.
• [FOR EACH ROW] : Specifies that the trigger should be executed for each row in the table. If omitted, the trigger will be executed only once.
• : The table to which the trigger is attached.
• : Events that trigger a trigger, such as INSERT , UPDATE , or DELETE .
• : SQL statements executed by the trigger.

Trigger example

The following example creates a trigger that updates last_updated column when a new record is inserted in the customers table:

 <code class="sql">CREATE TRIGGER trg_customers_update BEFORE INSERT ON customers FOR EACH ROW AS BEGIN :NEW.last_updated := SYSDATE; END;</code>

This trigger sets last_updated column to the system date before inserting a new record.

Notice:

• Triggers can also use PL/SQL blocks for more complex operations.
• Oracle supports a variety of triggers, including Row , Statement , and System triggers.
• When creating a trigger, the performance impact and the expected consequences of the trigger behavior should be considered.

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