PostgreSQL NANOID

postgres-nanoid.sql

CREATE FUNCTION "nanoid"("size" int4 DEFAULT 21)
RETURNS text
  LANGUAGE plpgsql
  STABLE
AS
$$
DECLARE
  id text := '';
  i int := 0;
  urlAlphabet char(64) := 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ-_0123456789';
  bytes bytea := gen_random_bytes(size);
  byte int;
  pos int;
BEGIN
  WHILE i < size LOOP
    byte := get_byte(bytes, i);
    pos := (byte & 63) + 1; -- + 1 because substr starts at 1
    id := id || substr(urlAlphabet, pos, 1);
    i = i + 1;
  END LOOP;
  RETURN id;
END
$$
;

Conceptually based on https://github.com/ai/nanoid