PL/pgSQL allows us to make a trigger function. This trigger function is similar to an ordinary function but it does not have any parameter and has a return type trigger. A trigger fires when a condition is met and executes a special type of stored procedure called a trigger function.
PostgreSQL will call a trigger function when changes are being made to a particular table. The function must either return NULL or a row that matches the structure of the table for which the trigger function has been called.
As mentioned earlier, the trigger function is created as an ordinary function. The following is the syntax to create this:
CREATE FUNCTION trigger_function() RETURN trigger AS
The trigger function receives data about their calling environment through a special structure called TriggerData, which contains a set of local variables. For example, OLD and NEW represent the states of a row in the table before or after the triggering event. PostgreSQL provides other local...