Question

I have 3 fields in an employees table: personal_id, personal_id_type, and date_registered.

I need to find all the rows, one row for each personal_id + personal_id_type (here is where I think I can use a GROUP), but since there may be many entries for the same personal_id + personal_id_type (because employees can quit and get hired again later), I need to fetch only the newest entry (order by date_registered DESC).

Is this conceptually correct? What would be the syntax for grouping by 2 fields? Will I achieve what I need with that?

Edit: I’m sorry, actually there are a lot of fields, so I need the newest row, not only the newest date.

Answer 1

Find the newest date for every (personal_id, personal_id_type) combination in a subquery, then join to the original table:

SELECT
    e.*
FROM
    employees e
  JOIN   
    ( SELECT
          personal_id
        , personal_id_type
        , MAX(date_registered) AS latest_date_registered
      FROM
          employees
      GROUP BY
          personal_id
        , personal_id_type
    ) AS grp
    ON  grp.personal_id = e.personal_id
    AND grp.personal_id_type = e.personal_id_type
    AND grp.latest_date_registered = e.date_registered