PostgreSQL · January 2, 2024

PostgreSQL Command: CREATE EVENT TRIGGER

PostgreSQL Command: CREATE EVENT TRIGGER

PostgreSQL is a powerful open-source relational database management system that offers a wide range of features and functionalities. One of the key features of PostgreSQL is the ability to create event triggers, which allow users to define custom actions that are automatically executed in response to specific events occurring within the database.

What is an Event Trigger?

An event trigger is a named object in PostgreSQL that is associated with a specific event type. When the specified event occurs, the trigger function associated with the event trigger is executed. Event triggers provide a way to extend the functionality of PostgreSQL by allowing users to define custom actions that are triggered by events such as database creation, table creation, or even specific SQL statements.

Creating an Event Trigger

The CREATE EVENT TRIGGER command is used to create an event trigger in PostgreSQL. The basic syntax for creating an event trigger is as follows:

CREATE EVENT TRIGGER trigger_name
    ON event_type
    [ WHEN filter_condition ]
    EXECUTE FUNCTION trigger_function();

Let's break down the different components of the CREATE EVENT TRIGGER command:

  • trigger_name: This is the name of the event trigger that you want to create. It should be unique within the database.
  • event_type: This specifies the type of event that the trigger is associated with. PostgreSQL provides a wide range of event types, including database-related events (e.g., database creation, database deletion), table-related events (e.g., table creation, table deletion), and statement-related events (e.g., specific SQL statements).
  • filter_condition (optional): This allows you to specify a condition that must be met for the trigger function to be executed. If the condition evaluates to TRUE, the trigger function is executed; otherwise, it is skipped.
  • trigger_function: This is the name of the function that is executed when the event trigger is fired. The function must be defined in the database and should have the appropriate parameters and return type based on the event type.

Example: Creating an Event Trigger

Let's say we want to create an event trigger that automatically logs the creation of new tables in our PostgreSQL database. We can achieve this by creating an event trigger associated with the ddl_command_end event type, which is triggered after the execution of any DDL (Data Definition Language) command.

Here's an example of how we can create the event trigger:

CREATE EVENT TRIGGER log_table_creation
    ON ddl_command_end
    EXECUTE FUNCTION log_table_creation_function();

In this example, we assume that the log_table_creation_function() function is already defined in the database. This function can be implemented to perform any desired action, such as logging the table creation details to a separate table or sending a notification to the database administrator.

Summary

PostgreSQL's CREATE EVENT TRIGGER command allows users to define custom actions that are automatically executed in response to specific events occurring within the database. Event triggers provide a powerful way to extend the functionality of PostgreSQL and automate various tasks. By creating event triggers, users can define custom actions that are triggered by events such as database creation, table creation, or specific SQL statements.

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