Exploring Different Types of Oracle Triggers（oracle触发器类型）

The Oracle Database provides many different tools to help developers achieve the desired effects. One of these tools are triggers. Triggers allow developers to automatically execute commands or instructions when certain conditions or criteria within the database have been met. As a result, triggers can be an indispensable tool for any Oracle Database developer, and understanding them can be extremely beneficial. This article will explore the different types of Oracle triggers and how to use them.

There are two main types of triggers in Oracle databases: row and statement triggers. Row triggers are used to apply commands to individual rows when an action is taken on them. For example, we could create a row trigger on an employees table that triggers an insert command on a related log table whenever someone inserts or updates a row in the employees table. This can help keep track of changes to the database. The command for a row trigger looks something like this:

CREATE TRIGGER trigger_name BEFORE INSERT OR UPDATE ON employees 
    FOR EACH ROW
    BEGIN 
        INSERT INTO log_table (column_names) 
            VALUES ( column_values ); 
    END; 
/ 

The other type of trigger are statement triggers. Statement triggers are designed to fire when a statement is issued with the same name as the trigger itself. For example, we could create a trigger on an orders table that triggers an insert statement in a related log table whenever someone issues an orders statement. The command for a statement trigger looks something like this:

CREATE OR REPLACE TRIGGER tr_orders_log 
    BEFORE INSERT ON orders 
    FOR EACH ROW 
    BEGIN 
        INSERT INTO orders_log 
            (column_names) 
            VALUES ( column_values ); 
     END; 
/ 

In addition to the two types of triggers mentioned above, Oracle also provides two other trigger types: system triggers and compound triggers. System triggers are triggered whenever the system experiences an event such as start up or shut down. Compound triggers are useful when developers need to have multiple triggers fired off at the same time.

Using triggers can be a powerful and effective way to automatically manage complex processes within the Oracle Database. With the different types of triggers available to developers, they can find the best one to fit their needs. It is important to understand the different types of triggers, their uses, and the commands needed to create them. With the proper knowledge and understanding, Oracle triggers can help make complex tasks easier to manage and automate.