在 mysql 中使用 JOIN 语句获取最后插入的行

Question

我正在尝试使用 mysql 和 php 创建一个简单的问题跟踪器。用户可以在 tracker table 中输入详细信息，它会立即添加到 tracker 和 statusmapping table 中。

稍后用户可以更改 'status'，然后将其添加（不更新）到 statusmapping table.

我想合并这两个 table 并获得输出。当我得到输出时，我想从给定 id 的 statusmapping table 中获取最后插入的数据。

我的trackertable

+------------+---------+------------+----------------------+------------------------------------------------------+----------------------+
| tracker_id | tasksid | pagenameid | tracker_summary      | tracker_comment                                      | tracker_created_date |
+------------+---------+------------+----------------------+------------------------------------------------------+----------------------+
|         14 |       2 |          8 | some summary         | some comment to display for the buggy page.          | 2018-10-14 13:05:31  |
|         15 |       4 |          4 | revision for the faq | revision for the faq page and the comment goes here. | 2018-10-14 14:09:27  |
+------------+---------+------------+----------------------+------------------------------------------------------+----------------------+

和statusmappingtable。第二列 trackerid 是 FK 对应 tracker table.

+------------------+-----------+----------+---------------------+----------------------+
| statusmapping_id | trackerid | statusid | statusmapping_date  | statusmapping_reason |
+------------------+-----------+----------+---------------------+----------------------+
|                4 |        14 |        1 | 2018-10-14 13:05:31 | Newly opened!        |
|                5 |        14 |        2 | 2018-10-14 13:34:04 | This issue is closed |
|                6 |        15 |        1 | 2018-10-14 14:09:27 | Newly opened!        |
+------------------+-----------+----------+---------------------+----------------------+

到目前为止我试过了。我得到 NULL 列 statusid。但是最后插入的id是statusmappingtable中的2。我怎么得到那个。

SELECT 
trk.tracker_id, 
trk.tracker_summary, trk.tracker_comment,
stm.statusid
FROM trackers trk
LEFT JOIN statusmapping stm ON trk.tracker_id = (SELECT MAX(trackerid) FROM `statusmapping`)
GROUP BY trk.tracker_id

这是输出。

+------------+----------------------+------------------------------------------------------+----------+
| tracker_id | tracker_summary      | tracker_comment                                      | statusid |
+------------+----------------------+------------------------------------------------------+----------+
|         14 | some summary         | some comment to display for the buggy page.          |     NULL |
|         15 | revision for the faq | revision for the faq page and the comment goes here. |        1 |
+------------+----------------------+------------------------------------------------------+----------+

Answer 1

在单独的 Derived Table 中，您可以获得 tracker_id 的最后更新日期时间。使用该值连接到主表，以获取 tracker_id.

尝试以下操作：

SELECT 
  trk.tracker_id, 
  trk.tracker_summary, 
  trk.tracker_comment,
  stm.statusid
FROM trackers trk
INNER JOIN statusmapping stm 
  ON trk.tracker_id = stm.trackerid 
INNER JOIN (SELECT trackerid, 
                  MAX(statusmapping_date) AS max_statusmapping_date 
           FROM statusmapping 
           GROUP BY trackerid) AS dt 
  ON dt.trackerid = trk.tracker_id AND 
     dt.max_statusmapping_date = stm.statusmapping_date

在 mysql 中使用 JOIN 语句获取最后插入的行

Get the last inserted row using JOIN statement in mysql

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database

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