postgresqlHow do I create a PostgreSQL trigger?

Creating a trigger in PostgreSQL requires a few steps:

1. Create a function to execute when the trigger is fired. This function should accept the same parameters as the trigger.

   CREATE FUNCTION my_trigger_function()
   RETURNS trigger AS $$
   BEGIN
   -- Your code goes here
   END;
   $$ LANGUAGE plpgsql;

2. Create the trigger itself, specifying the table and event it should fire on, as well as the function to execute.

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

3. Optionally, you can specify the timing of the trigger (BEFORE or AFTER) and the type of event (INSERT, UPDATE, or DELETE).

4. Optionally, you can also specify the conditions under which the trigger should fire using a WHEN clause.

   CREATE TRIGGER my_trigger
   AFTER INSERT ON my_table
   FOR EACH ROW
   WHEN (NEW.status = 'active')
   EXECUTE PROCEDURE my_trigger_function();

5. Finally, you can enable and disable the trigger using the ENABLE and DISABLE commands, respectively.

   ENABLE TRIGGER my_trigger ON my_table;

For more information, please see the PostgreSQL documentation.

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