MySQL 查询 - 加入子查询

Question

我有什么

我有多个这样的表：

tbl_hw_inventar (hw_id, hostname, hw_typ_idfs, hw_created_user_idfs, etc...)

tbl_hw_typ (hw_typ_id, hw_typ_title, etc...)

tbl_user (user_id,username, etc...)

tbl_hw_edited (hw_edited_id, hw_edited_client_idfs, hw_edited_date, hw_edited_user_idfs)

我需要什么

我想输出一个 table 包含以下信息：

 hw_id | Hostname | created                         | last edited 

 12315 | client-01 | 2015-05-06 15:31:06 (username) | 2015-07-02 09:46:17 (username) |

问题

如您所见，我可以通过外键和 内连接 获得类似 hw_typ 的信息“tbl_hw_typ”。对于带有“hw_created_user_idfs”的信息和获取 username 的 username 与 userid.

的信息相同

但是我怎样才能得到上次编辑、日期时间和用户名？

在我的 table“tbl_hw_edited”中，我有这样的条目：

row id | hw_id | datetime | user_id

代码

到目前为止，我的 SQL 查询如下所示：

SELECT `tbl_hw_inventar`.*, `tbl_hw_typ`.`hw_typ_title`, `tbl_user`.`username`, `tbl_hw_edited`.`hw_edited_id` 
FROM `tbl_hw_inventar` 
INNER JOIN `tbl_hw_typ` 
ON `tbl_hw_inventar`.`hw_typ_idfs` = `tbl_hw_typ`.`hw_typ_id` 
INNER JOIN `tbl_user` 
on `tbl_hw_inventar`.`hw_create_user_idfs` = `tbl_user`.`id`
JOIN (
    SELECT MAX(`tbl_hw_edited`.`hw_edited_id`), `tbl_hw_edited`.`hw_edited_client_idfs`
    FROM `tbl_hw_edited`
    ) `tbl_hw_edited` ON `tbl_hw_inventar`.`hw_id` = `tbl_hw_edited`.`hw_edited_client_idfs`
ORDER BY `tbl_hw_inventar`.`hw_id` ASC

那么如何导出信息呢？看起来我必须在查询中进行子查询。但是我每次尝试都失败了。

谢谢你的帮助

编辑

按照建议，我将为每个 table:

提供更多信息（table 数据）

-tbl_hw_inventar-
| hw_id | hw_hostname | hw_create_date      | hw_create_user_idfs |
| 1     | client-01   | 2015-03-06 11:57:42 | 1                   |
| 2     | client-02   | 2015-09-21 21:17:00 | 3                   |

-tbl_hw_edited-
| hw_edited_id | hw_edited_client_idfs | hw_edited_date      | hw_edited_user_idfs |
| 1            | 1                     | 2015-09-24 17:30:22 | 1                   |
| 2            | 2                     | 2015-09-24 16:33:22 | 2                   |
| 3            | 1                     | 2015-09-24 23:30:22 | 2                   |
| 4            | 2                     | 2015-09-24 20:30:22 | 3                   |

-tbl_user-
| id | username |
| 1  | ismaelw  |
| 2  | skalb    |
| 3  | yrumpel  |

因此，作为最终结果，我需要这样的输出：

| hw_id | hostname  | created                       | edited                      |
| 1     | client-01 | 2015-03-06 11:57:42 (ismaelw) | 2015-09-24 23:30:22 (skalb) |

Answer 1

如果我正确解释了你的 table，你需要找到每个 hw_edited_client_idfs（连接到 hw_id）的最大（编辑日期）

                            SELECT
                                  hw_edited_client_idfs
                                , MAX(hw_edited_date) AS last_edit_dt
                            FROM tbl_hw_edited
                            GROUP BY hw_edited_client_idfs

根据该结果，您可以将其返回到源 table，以发现哪个用户与最大（编辑日期）相关联

                SELECT
                      het.*
                FROM tbl_hw_edited AS het
                      INNER JOIN (
                            SELECT
                                  hw_edited_client_idfs
                                , MAX(hw_edited_date) AS last_edit_dt
                            FROM tbl_hw_edited
                            GROUP BY hw_edited_client_idfs
                      ) AS mx ON het.hw_edited_client_idfs = mx.hw_edited_client_idfs
                                  AND het.hw_edited_date = mx.last_edit_dt

然后这个结果像这样使用：

SELECT
      i.hw_id
    , i.hw_hostname
    , uc.username created_by
    , he.hw_edited_date last_edit_date
    , ue.username last_edit_by
FROM tbl_hw_inventar AS i
      INNER JOIN tbl_user AS uc ON i.hw_create_user_idfs = uc.id
      LEFT OUTER JOIN (
                SELECT
                      het.*
                FROM tbl_hw_edited AS het
                      INNER JOIN (
                            SELECT
                                  hw_edited_client_idfs
                                , MAX(hw_edited_date) AS last_edit_dt
                            FROM tbl_hw_edited
                            GROUP BY hw_edited_client_idfs
                      ) AS mx ON het.hw_edited_client_idfs = mx.hw_edited_client_idfs
                                  AND het.hw_edited_date = mx.last_edit_dt
          ) AS he ON i.hw_id = he.hw_edited_client_idfs
      LEFT OUTER JOIN tbl_user AS ue ON he.hw_edited_user_idfs = ue.id

产生这个结果：

| hw_id | hw_hostname | username |              hw_edited_date | username |
|-------|-------------|----------|-----------------------------|----------|
|     1 |   client-01 |  ismaelw | September, 24 2015 23:30:22 |    skalb |
|     2 |   client-02 |  yrumpel | September, 24 2015 20:30:22 |  yrumpel |

见this sqlfiddle

MySQL 查询 - 加入子查询

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