uuid generator for uuid v7(draft3)

uuid_v7_draft3.sql

-- generator function for UUID v7 (draft3).
-- https://datatracker.ietf.org/doc/html/draft-peabody-dispatch-new-uuid-format-03
-- it also depends on gen_random_uuid.
create or replace function uuid_v7() returns uuid as $$
declare
    l_unixts_text text := lpad(
        to_hex(
            (
                extract(epoch from clock_timestamp()) * 1000
            )::bigint & x'FFFFFFFFFFFF'::bigint
        ), 12, '0');
begin
    return (
        substring(l_unixts_text from 1 for 8)
        || '-'
        || substring(l_unixts_text from 9 for 4)
        || '-7'
        || substring(gen_random_uuid()::text from 16 for 21))::uuid;
end $$ language plpgsql;