In PostgreSQL, the Drop function statement is used to remove a function.
Syntax: drop function [if exists] function_name(argument_list) [cascade | restrict]
Let’s analyze the above syntax:
- First, specify the name of the function that you want to remove after the drop function keywords.
- Second, use the if exists option if you want to instruct PostgreSQL to issue a notice instead of an error in case the function does not exist.
- Third, specify the argument list of the function. Since functions can be overloaded PostgreSQL needs to know which function you want to remove by checking the argument list. If a function is unique within the schema, you do not need to specify the argument list.
When a function has any dependent objects such as operators or triggers, you cannot drop that function. To drop the function and its dependent objects, you need to specify the cascade option. The drop function with the cascade option will recursively remove the function, its dependent objects, and the objects that depend on those objects, and so on.
By default, the drop function statement uses the restrict option that rejects the removal of a function when it has any dependent objects. To drop multiple functions using a single drop function statement, you specify a comma-separated list of function name after the drop function keyword like this:
drop function [if exists] function1, function2, ...;
For the sake of example, we will use the sample database ie, dvdrental.
The following statement uses the create function statement to define a function that returns a set of films including film_id, title, and actor:
create or replace function get_film_actors() returns setof record as $$ declare rec record; begin for rec in select film_id, title, (first_name || ' ' || last_name)::varchar from film inner join film_actor using(film_id) inner join actor using (actor_id) order by title loop return next rec; end loop; return; end; $$ language plpgsql;
The following statement defines a function with the same name get_film_actors. However, it accepts a film id as the argument:
create or replace function get_film_actors(p_fiml_id int) returns setof record as $$ declare rec record; begin for rec in select film_id, title, (first_name || ' ' || last_name)::varchar from film inner join film_actor using(film_id) inner join actor using (actor_id) where film_id = p_fiml_id order by title loop return next rec; end loop; return; end; $$ language plpgsql;
The following statement attempts to drop the get_film_actors function:
drop function get_film_actors;
Since the get_film_actors stored procedure is not unique, you need to specify which function you want to drop.
The following statement drops the get_film_actors function that has zero parameters:
drop function get_film_actors();
Now, there is only one get_film_actors function left. Since it is unique in the database, you can drop it without specifying its argument list like this:
drop function get_film_actors;
Or if you want to specify the exact function, you can use the following statement:
drop function get_film_actors(int);
- Use the drop function statement to remove a function.
- Specify the argument list in the function if the function is overloaded.
- Use the drop function statement with the cascade option to drop a function and its dependent objects and objects that depends on those objects, and so on.