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# PostgreSQL Drop Function

**Summary**: in this tutorial, you will learn how to use the PostgreSQL `drop function` statement to remove a function.

## Introduction to PostgreSQL DROP FUNCTION statement

To remove a user-defined function, you use the `drop function` statement.

Here's the syntax of the `drop function` statement:

```plsql
drop function [if exists] function_name(argument_list)
[cascade | restrict]
```

In this 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 if the function does not exist.
- Third, specify the argument list of the function. Since [functions can be overloaded,](https://neon.com/postgresql/postgresql-plpgsql/plpgsql-function-overloading) 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](../postgresql-triggers), you cannot drop that function.

To drop the function and its dependent objects, you can use 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 names after the `drop function` keyword like this:

```plsql
drop function [if exists] function1, function2, ...;
```

## PostgreSQL Drop Function examples

The following statement uses the [`create function`](https://neon.com/postgresql/postgresql-plpgsql/postgresql-create-function) statement to define a function that returns a set of films including `film_id`, `title`, and `actor`:

```plsql
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:

```plsql
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:

```plsql
drop function get_film_actors;
```

PostgreSQL issued an error:

```
ERROR:  function name "get_film_actors" is not unique
HINT:  Specify the argument list to select the function unambiguously.
SQL state: 42725
```

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:

```plsql
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:

```plsql
drop function get_film_actors;
```

Alternatively, if you want to specify the exact function, you can use the function name with the argument list:

```plsql
drop function get_film_actors(int);
```

## Summary

- Use the `drop function` statement to delete a function from a database.
- 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 depend on those objects, and so on.

---

## Related docs (PostgreSQL PL/pgSQL)

- [Introduction](https://neon.com/postgresql/postgresql-plpgsql/introduction-to-postgresql-stored-procedures)
- [Block Structure](https://neon.com/postgresql/postgresql-plpgsql/plpgsql-block-structure)
- [Variables](https://neon.com/postgresql/postgresql-plpgsql/plpgsql-variables)
- [Constants](https://neon.com/postgresql/postgresql-plpgsql/plpgsql-constants)
- [IF-ELSE Statements](https://neon.com/postgresql/postgresql-plpgsql/plpgsql-if-else-statements)
- [CASE Statement](https://neon.com/postgresql/postgresql-plpgsql/plpgsql-case-statement)
- [Loop Statements](https://neon.com/postgresql/postgresql-plpgsql/plpgsql-loop-statements)
- [FOR Loop](https://neon.com/postgresql/postgresql-plpgsql/plpgsql-for-loop)
- [WHILE Loop](https://neon.com/postgresql/postgresql-plpgsql/pl-pgsql-while-loop)
- [EXIT Statement](https://neon.com/postgresql/postgresql-plpgsql/plpgsql-exit)
- [CONTINUE Statement](https://neon.com/postgresql/postgresql-plpgsql/pl-pgsql-continue)
- [Cursor](https://neon.com/postgresql/postgresql-plpgsql/plpgsql-cursor)
- [Function Parameters](https://neon.com/postgresql/postgresql-plpgsql/plpgsql-function-parameters)
- [Function Overloading](https://neon.com/postgresql/postgresql-plpgsql/plpgsql-function-overloading)
- [Function Returns Table](https://neon.com/postgresql/postgresql-plpgsql/plpgsql-function-returns-a-table)
- [Returns SETOF](https://neon.com/postgresql/postgresql-plpgsql/plpgsql-returns-setof)
- [Record Types](https://neon.com/postgresql/postgresql-plpgsql/plpgsql-record-types)
- [Row Types](https://neon.com/postgresql/postgresql-plpgsql/pl-pgsql-row-types)
- [Error Messages](https://neon.com/postgresql/postgresql-plpgsql/plpgsql-errors-messages)
- [Exception Handling](https://neon.com/postgresql/postgresql-plpgsql/postgresql-exception)
- [CREATE FUNCTION](https://neon.com/postgresql/postgresql-plpgsql/postgresql-create-function)
- [CREATE PROCEDURE](https://neon.com/postgresql/postgresql-plpgsql/postgresql-create-procedure)
- [DROP PROCEDURE](https://neon.com/postgresql/postgresql-plpgsql/postgresql-drop-procedure)
- [Stored Procedure with INOUT Parameters](https://neon.com/postgresql/postgresql-plpgsql/postgresql-stored-procedure-with-inout-parameters)
- [Introduction to Stored Procedures](https://neon.com/postgresql/postgresql-plpgsql/introduction-to-postgresql-stored-procedures)
- [SELECT INTO](https://neon.com/postgresql/postgresql-plpgsql/pl-pgsql-select-into)
- [ASSERT Statement](https://neon.com/postgresql/postgresql-plpgsql/pl-pgsql-assert)
- [Dollar-Quoted String Constants](https://neon.com/postgresql/postgresql-plpgsql/dollar-quoted-string-constants)