如何按2个字段分组并同时按日期排序? [英] How to group by 2 fields and order by date at the same time?

问题描述

我在employees表中有3个字段:personal_id，personal_id_type和date_registered.

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

我需要找到所有行，每个personal_id + personal_id_type行(在这里我可以使用GROUP)，但是由于同一personal_id + personal_id_type可能有很多条目(因为员工可以辞职并以后再被雇用)，我只需要获取最新的条目(order by date_registered DESC).

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).

从概念上讲这是正确的吗?按2个字段分组的语法是什么?我会满足我的需求吗?

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

很抱歉，实际上有很多字段，所以我需要最新的行，而不仅仅是最新的日期.

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

推荐答案

在子查询中查找每个(personal_id, personal_id_type)组合的最新日期，然后加入原始表:

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

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