[minitech]

  > SELECT *
  > FROM external_api
  > WHERE id = :my_id 
  >   AND sync_token = (SELECT max(sync_token) FROM ext_api WHERE id = :my_id)

Does this have an advantage over

  SELECT * FROM external_api
    WHERE id = :my_id
    ORDER BY sync_token DESC
    LIMIT 1

? Assuming the index is on (id, sync_token).

[sa46]

For my specific setup and a single row lookup, the ORDER BY ... LIMIT 1 is faster (0.1 ms vs. 1.2 ms).

The ORDER BY ... LIMIT 1 one is the same as the DISTINCT ON query, but the DISTINCT ON can return more than one resource.