Nano ID implementation in PostgreSQL - PL/pgSQL

nanoid.sql

CREATE EXTENSION IF NOT EXISTS pgcrypto;

CREATE OR REPLACE FUNCTION public.nanoid(size integer DEFAULT 21)
 RETURNS text
 LANGUAGE plpgsql
 STABLE
AS $function$
DECLARE
  id text := '';
  i int := 0;
  urlAlphabet char(64) := '_-0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz';
  bytes bytea := gen_random_bytes(size);
  byte int;
  pos int;
BEGIN
  WHILE i < size LOOP
    byte := get_byte(bytes, i);
    pos := (byte & 63) + 1;
    id := id || substr(urlAlphabet, pos, 1);
    i = i + 1;
  END LOOP;
  RETURN id;
END
$function$