试试这个方法：

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.

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如果到达这里，因为你的function给了你同样的错误（像我一样）..这里有一个过度烘焙的例子，使用一个函数来更新右下角的tweet“blurb”与“hello world”。

重要提示：语言在最后一个空格之前（见下文）。这在可接受的解决方案中很容易被忽略。

| ID（序列号）|pub_id（text）|tweet（文本）|
| --|--|--|
| 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         |
  --------------------------------------------------
*/

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下面是同样的错误：
错误：未指定语言
当我创建PL/pgSQL function时，如下所示：

CREATE FUNCTION my_func() RETURNS INTEGER AS $$
BEGIN
RETURN 2;
END;
$$;

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所以，我设置LANGUAGE plpgsql如下所示，然后错误就解决了：

CREATE FUNCTION my_func() RETURNS INTEGER AS $$
BEGIN
RETURN 2;
END; -- ↓ Here ↓
$$ LANGUAGE plpgsql;

型
或者：

CREATE FUNCTION my_func() RETURNS INTEGER LANGUAGE plpgsql AS $$
BEGIN                                    -- ↑ ↑ Here ↑ ↑
RETURN 2;
END;
$$;

型