How to create a postgres function that returns a value

Question

I am trying to move some of my web app logic into postgres functions. But I am hitting some errors while creating a very basic insert function.

This is the function that I am trying to create;

CREATE OR REPLACE FUNCTION create_user(IN email EMAIL, password TEXT, thumb TEXT)
RETURNS text AS 
$BODY$
BEGIN
   insert into users (unqid, thumb, email, password) 
   values (gen_random_uuid(), thumb, email, password)
   returning unqid ;
END;
$BODY$
  LANGUAGE plpgsql
  VOLATILE

I am trying to get the function to return the uuid of the item if the insert is successful. And I am calling it like this;

select * from create_user('newuser@mail.com', 'passpopcorn', 'thumbelinaurl');

Getting this error;

SQL Error [42601]: ERROR: query has no destination for result data
  Where: PL/pgSQL function create_user(email,text,text) line 3 at SQL statement

From my googling it sounds like this error comes up when you don't have a return statement in the query. But in my Insert query, I do have a returning statement.

Extra question; for simple insert statements (like this one here, or one with a couple of select followed by an insert), would functions be a better bet or procedures?

Answer 1

SQL Error [42601]: ERROR: query has no destination for result data

insert ... returning ... produces a result set that contains columns referenced in the returning clause. In a PL/pgSQL block that result set must be dealt with somehow. You have three options:

• An intermediate variable

    CREATE OR REPLACE FUNCTION create_user(IN email EMAIL, password TEXT, thumb TEXT)
    RETURNS VARCHAR(40) AS 
    $BODY$
    DECLARE id VARCHAR(40);
    BEGIN
       insert into users (unqid, thumb, email, password) 
       values (gen_random_uuid(), thumb, email, password)
       returning unqid INTO id;
       RETURN id;
    END;
    $BODY$
      LANGUAGE plpgsql
      VOLATILE  
  

• return query, which avoids an extra variable

    CREATE OR REPLACE FUNCTION create_user(IN email EMAIL, password TEXT, thumb TEXT)
    RETURNS TABLE (id VARCHAR(40)) AS 
    $BODY$
    BEGIN
       RETURN QUERY 
       insert into users (unqid, thumb, email, password) 
       values (gen_random_uuid(), thumb, email, password)
       returning unqid;
    END;
    $BODY$
      LANGUAGE plpgsql
      VOLATILE  
  

• A simple SQL function, which I would prefer in your case as you don't need any PL/pgSQL functionality as it stands

    CREATE OR REPLACE FUNCTION create_user(IN email EMAIL, password TEXT, thumb TEXT)
    RETURNS TABLE (id VARCHAR(40)) AS 
    $BODY$
       insert into users (unqid, thumb, email, password) 
       values (gen_random_uuid(), thumb, email, password)
       returning unqid;
    $BODY$
      LANGUAGE SQL
  

Answer 2

A function basically replaces a fixed values when used as you do

so your code would look like

CREATE TABLE users (unqid varchar(64), thumb TEXT, email TEXT, password TEXT) 

CREATE OR REPLACE FUNCTION create_user(IN email TEXT, password TEXT, thumb TEXT)
RETURNS text AS 
$BODY$
DECLARE _unqid varchar(64);
BEGIN
   
 _unqid = gen_random_uuid();
   insert into users (unqid, thumb, email, password) 
   values (_unqid, thumb, email, password);
   RETURN  _unqid ;
END;
$BODY$
  LANGUAGE plpgsql
  VOLATILE

select create_user('newuser@mail.com', 'passpopcorn', 'thumbelinaurl')

| create_user                          |
| :----------------------------------- |
| 759f4da9-bc17-4349-be4c-34e9b76fb78b |

SELECT * FROM users

unqid                                | thumb         | email            | password   
:----------------------------------- | :------------ | :--------------- | :----------
759f4da9-bc17-4349-be4c-34e9b76fb78b | thumbelinaurl | newuser@mail.com | passpopcorn

db<>fiddle here