Function for generating random-based UUIDs (v4) on PostgreSQL

fn_uuid_random_based.sql

/**
 * Generate a random-based UUID (v4)
 *
 * RFC-4122 compliant.
 *
 * Tags: uuid guid uuid-generator guid-generator generator random rfc4122 rfc-4122
*/
create or replace function fn_uuid_random_based() returns uuid as $$
declare
	v_bytes  bytea;
begin

	-- generate a pseudo random byte array
	v_bytes := decode(md5(clock_timestamp()::text || random()::text || random()::text), 'hex');

	-- Set version bits (0100)
	v_bytes := set_bit(v_bytes, 55, 0);
	v_bytes := set_bit(v_bytes, 54, 1);
	v_bytes := set_bit(v_bytes, 53, 0);
	v_bytes := set_bit(v_bytes, 52, 0);

	-- Set variant bits (10xx)
	v_bytes := set_bit(v_bytes, 71, 1);
	v_bytes := set_bit(v_bytes, 70, 0);

	return encode(v_bytes, 'hex')::uuid;

end $$ language plpgsql;

-- EXAMPLE:
-- 
-- select fn_uuid_random_based() uuid, clock_timestamp()-statement_timestamp() time_taken;
-- 
-- |uuid                                  |time_taken        |
-- |--------------------------------------|------------------|
-- |3a901c1c-5aaf-488a-9a94-55e6cf933cab  |00:00:00.000189   |
--