Postgres trigger creation - ERROR: no language specified SQL state: 42P13 - sql

Question

I am new to triggers. I am trying to create a trigger by following this link - http://www.postgresqltutorial.com/creating-first-trigger-postgresql/. But it gives some error. The code block and the error is given below.
Code block:
CREATE OR REPLACE FUNCTION log_last_name_changes()
RETURNS trigger AS
$BODY$
BEGIN
IF NEW.last_name <> OLD.last_name THEN
INSERT INTO employee_audits(employee_id,last_name,changed_on)
VALUES(OLD.id,OLD.last_name,now());
END IF;
RETURN NEW;
END;
$BODY$
And the error:
ERROR: no language specified
SQL state: 42P13
What can I try next?

Answer 1

Try this way:
CREATE OR REPLACE FUNCTION log_last_name_changes()
RETURNS trigger AS
$BODY$
BEGIN
IF NEW.last_name <> OLD.last_name THEN
INSERT INTO employee_audits(employee_id,last_name,changed_on)
VALUES(OLD.id,OLD.last_name,now());
END IF;
RETURN NEW;
END;
$BODY$
LANGUAGE plpgsql VOLATILE -- Says the function is implemented in the plpgsql language; VOLATILE says the function has side effects.
COST 100; -- Estimated execution cost of the function.

Answer 2

If arriving here because your function gave you the same error (like mine did).. here's an over-baked example of using a function to update the tweet on the bottom right "blurb" with "hello world".
Important note: language goes BEFORE the last semicolon (see below). This is easy to miss in the accepted solution.
id (serial)
pub_id (text)
tweet (text)
1
abc
hello world
2
def
blurb
-- Optional drop if replace fails below.
drop function if exists sync_tweets(text, text);
create or replace function sync_tweets(
src_pub_id text, -- function arguments
dst_pub_id text
) returns setof tweets as -- i.e. rows. int, text work too
$$
declare
src_id int; -- temp function variables (not args)
dest_id int;
src_tweet text;
begin
-- query result into a temp variable
src_id := (select id from tweets where pub_id = src_pub_id);
-- query result into a temp variable (another way)
select tweet into src_tweet from tweets where id = src_id;
dest_id := (select id from tweets where pub_id = dst_pub_id);
update tweets set tweet=src_tweet where id = dest_id;
return query -- i.e. rows, return 0 with return int above works too
select * from tweets where pub_id in (src_pub_id, dst_pub_id);
end
$$ language plpgsql; -- need the language to avoid ERROR 42P13
-- Run it!
select * from sync_tweets('abc', 'def');
/*
Outputs
__________________________________________________
| id (serial) | pub_id (text) | tweet (text) |
|---------------|-----------------|----------------|
| 1 | abc | hello world |
| 2 | def | blurb |
--------------------------------------------------
*/