How to Create A Trigger In Postgresql?

To create a trigger in PostgreSQL, you use the CREATE TRIGGER statement followed by the trigger name and the table or view to which the trigger will be attached. You also specify whether the trigger should be fired BEFORE or AFTER an event, such as an INSERT, DELETE, or UPDATE operation on the table.

Next, you define the trigger function that will be executed when the trigger is fired. This function can be written in PL/pgSQL or any other supported procedural language.

You can further customize the trigger by specifying conditions under which it should be activated using the WHEN clause.

Once the trigger is created, it will automatically be executed whenever the specified event occurs on the table or view. Triggers are a powerful tool in PostgreSQL that allow you to enforce data integrity, perform complex validation logic, audit changes, and more.

How to create a trigger in PostgreSQL that fires FOR EACH ROW?

To create a trigger in PostgreSQL that fires for each row, you need to specify the keyword "FOR EACH ROW" when defining the trigger. Here's an example of how you can create a trigger that fires for each row:

1
2
3
4

CREATE TRIGGER my_trigger
AFTER INSERT OR UPDATE ON my_table
FOR EACH ROW
EXECUTE FUNCTION my_function();

In this example:

• my_trigger is the name of the trigger.
• AFTER INSERT OR UPDATE ON my_table specifies the trigger to be executed after an INSERT or UPDATE operation on the my_table table.
• FOR EACH ROW specifies that the trigger should fire for each affected row.
• EXECUTE FUNCTION my_function() is the function that will be executed when the trigger fires.

Make sure to replace my_table with the actual table name and my_function() with the actual function that you want to execute when the trigger fires.

How to create a trigger in PostgreSQL that executes a stored procedure?

To create a trigger in PostgreSQL that executes a stored procedure, follow these steps:

1. Create a stored procedure in your database. For example, let's say you have a stored procedure named "my_procedure" that you want to execute when the trigger is activated:

1
2
3
4
5
6

CREATE OR REPLACE PROCEDURE my_procedure()
AS $$
BEGIN
  -- Your logic here
END;
$$ LANGUAGE plpgsql;

1. Create the trigger that will call the stored procedure when a specified event occurs. For example, let's create a trigger named "my_trigger" that will execute the "my_procedure" stored procedure when a row is inserted into the "my_table" table:

1
2
3
4
5

CREATE TRIGGER my_trigger
AFTER INSERT
ON my_table
FOR EACH ROW
EXECUTE PROCEDURE my_procedure();

1. Now, whenever a row is inserted into the "my_table" table, the "my_procedure" stored procedure will be executed automatically by the trigger "my_trigger".

You can customize the trigger to execute the stored procedure based on different events (e.g., UPDATE, DELETE) and conditions (e.g., specific columns being updated). Just make sure to replace the placeholder values (e.g., "my_procedure", "my_table") with your actual stored procedure and table names.

What is a trigger function in PostgreSQL?

A trigger function in PostgreSQL is a function that is automatically executed in response to certain events, such as insertion, update, or deletion of data in a table. Triggers are defined to enforce specific constraints, perform cascading updates, or execute additional logic when certain data changes occur. Trigger functions are written in PL/pgSQL, which is a procedural language supported by PostgreSQL, and are associated with specific tables to be executed when the specified events occur.

How to create a trigger in PostgreSQL that fires AFTER an UPDATE operation?

To create a trigger in PostgreSQL that fires after an UPDATE operation, you can follow these steps:

1. Connect to your PostgreSQL database using a SQL client or command line interface.
2. Use the following syntax to create a new trigger:

1
2
3
4

CREATE TRIGGER trigger_name
AFTER UPDATE ON table_name
FOR EACH ROW
EXECUTE FUNCTION function_name();

Replace trigger_name with the desired name for your trigger, table_name with the name of the table on which you want to create the trigger, and function_name with the name of the function that you want to execute when the trigger fires.

1. Define the function that you want to execute when the trigger fires. For example, you can create a function that logs information about the updated rows:

 1
 2
 3
 4
 5
 6
 7
 8
 9
10

CREATE FUNCTION log_update()
RETURNS TRIGGER
AS $$
BEGIN
  INSERT INTO audit_table (old_data, new_data, update_time)
  VALUES (OLD, NEW, now());
  RETURN NEW;
END;
$$
LANGUAGE plpgsql;

Replace audit_table with the name of the table where you want to log the update information. This function will insert the old and new data of the updated row, along with the timestamp of the update, into the audit_table.

1. After creating the function, you can now use it in the trigger by replacing function_name in the trigger creation statement with the name of the function you just created:

1
2
3
4

CREATE TRIGGER log_update_trigger
AFTER UPDATE ON your_table
FOR EACH ROW
EXECUTE FUNCTION log_update();

Replace log_update_trigger with the desired name for your trigger and your_table with the name of the table on which you want the trigger to fire.

1. Your trigger is now created and will execute the specified function after an UPDATE operation on the specified table.