This sounds like you're opening yourself up to situations where you have rows in data_journal that have status='Loading' but which have started_loading_at=NULL, in violation of your data model.

Your premise is slightly flawed in that your second example isn't actually difficult to write or understand as you claim. However, it could be argued that if the logic for selecting "loading" rows is repeated in multiple places then a layer of abstraction over it would be useful. This could be achieved in SQL by e.g.

    CREATE VIEW loading_entries AS
    SELECT * FROM data_journal 
    WHERE started_loading_at IS NOT NULL AND finished_loading_at IS NULL

or, if you have several such statuses you need to define,

    CREATE VIEW data_journal_view AS
    SELECT
    data_journal.*,
    CASE
      WHEN started_loading_at IS NOT NULL AND 
    finished_loading_at IS NULL THEN 'Loading'
      WHEN ... THEN ...
      ELSE 'Some other status'
    END AS status
    FROM data_journal