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('[email protected]', '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
  

• Rishav Sharan: is there any inherent benefit of using SQL functions over pl/pgsql ones?
• mustaccio: dba.stackexchange.com/questions/8119/function-performance

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('[email protected]', 'passpopcorn', 'thumbelinaurl')

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

SELECT * FROM users

unqid | thumb | email | password 
:----------------------------------- | :------------ | :--------------- | :----------
759f4da9-bc17-4349-be4c-34e9b76fb78b | thumbelinaurl | [email protected] | passpopcorn

db<>fiddle here