Postgres function for UUID v7 generation supporting microsecond precision. Lexicographic sortable, k-sortable, unique/collision-resistant UUIDs.

uuid_generate_v7.sql

-- Based off IETF draft, https://datatracker.ietf.org/doc/draft-peabody-dispatch-new-uuid-format/
-- and https://gist.github.com/kjmph/5bd772b2c2df145aa645b837da7eca74

create or replace function uuid_generate_v7()
returns uuid
as $$
declare
  unix_ts_ms bytea;
  uuid_bytes bytea;
begin
  unix_ts_ms = substring(int8send(floor(extract(epoch from clock_timestamp()) * 1000)::bigint) from 3);

  -- use random v4 uuid as starting point (which has the same variant we need)
  uuid_bytes = uuid_send(gen_random_uuid());

  -- overlay timestamp
  uuid_bytes = overlay(uuid_bytes placing unix_ts_ms from 1 for 6);

  -- set version 7
  uuid_bytes = set_byte(uuid_bytes, 6, (b'0111' || get_byte(uuid_bytes, 6)::bit(4))::bit(8)::int);

  return encode(uuid_bytes, 'hex')::uuid;
end
$$
language plpgsql
volatile;