When dealing with a Postgres database that stores internal products/assets, there is a chance that we will need either a unique EAN13 code for each or a UUID (Universal Unique Identifier), many times both of them.
For dealing with EAN13 (or alike data types) there is the "isn" module.
For dealing with UUIDs there are the "pgcrypto" and "uuid-ossp" modules.
If, whatever the reason, installing the aforementioned modules is a no go, then, for generating valid random EAN13 and UUID codes, the following Postgres custom functions will do the job.
Postgres custom function to generate random, valid EAN13 codes
CREATE OR REPLACE FUNCTION gen_ean13_random() RETURNS text AS $$ declare ean13 text; check_digit integer; begin ean13 = (SELECT string_agg(to_hex(width_bucket(random(), 0, 1, 10)-1) ,'') FROM generate_series(1, 12)); check_digit = (SELECT esum-mod(esum,10)+10-esum - CASE WHEN mod(esum,10) = 0 THEN 10 ELSE 0 END as ecd from (select sum( case when mod(row_number,2) = 0 THEN e::int * 3 ELSE e::int END) as esum from (select e, row_number() over() from unnest(regexp_split_to_array(ean13,'')) e) q) q1); ean13 = ean13||check_digit::TEXT; return ean13; end; $$ LANGUAGE plpgsql IMMUTABLE;
Postgres custom function to generate random, valid UUIDs
CREATE OR REPLACE FUNCTION gen_uuid_random()
RETURNS uuid AS
$$
SELECT string_agg(lpad(to_hex(width_bucket(random(), 0, 1, 256)-1),2,'0') ,'')::uuid FROM generate_series(1, 16);
$$
LANGUAGE sql IMMUTABLE;
Use them whenever you need, on-demand, or better, to automate things, within table triggers.