[英]MS Access SQL query from 3 tables
我在MS Access 2010中顯示以下3個表格:
表: 設備
id | device_id | Company | Version | Revision |
-----------------------------------------------
1 | dev_a | Almaras | 1.5.1 | 0.2A |
2 | dev_b | Enigma | 1.5.1 | 0.2A |
3 | dev_c | Almaras | 1.5.1 | 0.2C |
*Field: device_id is Primary Key Unique String
*Field ID is just an auto-number column
表:活動
id | act_id | act_date | act_type | act_note |
------------------------------------------------
1 | dev_a | 07/22/2013 | usb_axc | ok |
2 | dev_a | 07/23/2013 | usb_axe | ok | (LAST ROW for dev_a)
3 | dev_c | 07/22/2013 | usb_axc | ok | (LAST ROW for dev_c)
4 | dev_b | 07/21/2013 | usb_axc | ok | (LAST ROW for dev_b)
*Field: act_id contains device_id; NOT UNIQUE
*Field ID is just an auto-number column
表:矩陣
id | mat_id | tc | ts | bat | cycles |
-----------------------------------------
1 | dev_a | 2811 | 10 | 99 | 200 |
2 | dev_a | 2911 | 10 | 97 | 400 |
3 | dev_a | 3007 | 10 | 94 | 600 |
4 | dev_a | 3210 | 10 | 92 | 800 | (LAST ROW for dev_d)
5 | dev_b | 1100 | 5 | 98 | 100 |
6 | dev_b | 1300 | 8 | 93 | 200 |
7 | dev_b | 1411 | 11 | 90 | 300 | (LAST ROW for dev_b)
8 | dev_c | 4000 | 27 | 77 | 478 | (LAST ROW for dev_c)
*Field: mat_id contains device_id; NOT UNIQUE
*Field ID is just an auto-number column
有沒有什么方法可以查詢表以獲取結果,如下所示(設備中的每個設備,其他兩個表中的每個僅添加了最后一行[請參見示例輸出表]):
查詢結果:
device_id | Company | act_date | act_type | bat | cycles |
------------------------------------------------------------
device_a | Almaras | 07/23/2013 | usb_axe | 92 | 800 |
device_b | Enigma | 07/21/2013 | usb_axc | 90 | 300 |
device_c | Almaras | 07/22/2013 | usb_axc | 77 | 478 |
有任何想法嗎? 預先感謝您閱讀和幫助我:)
我想是你想要的
SELECT a.device_id, a.Company,
b.act_date, b.act_type,
c.bat, c.cycles
FROM ((((devices AS a
INNER JOIN activities AS b
ON a.device_id = b.act_id)
INNER JOIN matrix AS c
ON a.device_id = c.mat_id)
INNER JOIN
(
SELECT act_id, MAX(act_date) AS max_date
FROM activities
GROUP BY act_id
) AS d ON b.act_id = d.act_id AND b.act_date = d.max_date)
INNER JOIN
(
SELECT mat_id, MAX(tc) AS max_tc
FROM matrix
GROUP BY mat_id
) AS e ON c.mat_id = e.mat_id AND c.tc = e.max_tc)
子查詢: d
和e
分別獲取每個act_id
的最新行。
嘗試
SELECT devices.device_id, devices.Company, activities.act_data, activities.act_type, matrix.bat, matrix.cycles
FROM devices
LEFT JOIN activities
ON devices.device_id = activities.act_id
LEFT JOIN matrix
ON devices.device_id = matrix.mat_id;
您如何看待Matrix中的“最后”行?
您需要WHERE act_date in (SELECT max(a.act_date) from activities a where a.mat_id=d.device_id GROUP BY a.mat_id)
執行類似WHERE act_date in (SELECT max(a.act_date) from activities a where a.mat_id=d.device_id GROUP BY a.mat_id)
和連接矩陣相似。
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