Question

我有两个表格，其中包含有关我在查询中加入的图形的信息。第一个表包含图纸的唯一编号，标题和绘制对象。第二个表包含修订版和图纸修订日期。

表1

|dwg_id|project_no|sws_dwg_no|dwg_title|dwg_by|
|1     |153       |153-100   |Pipe...  |JS    |

表2

|dwg_id|dwg_rev|dwg_date            |rev_id|
|1     |A      |2015-07-15 11:00:00 |1     |
|1     |B      |2015-07-23 12:00:00 |2     |
|1     |C      |2015-08-06 10:00:00 |3     |

我想加入两个表，只显示绘图的最新版本更改。

这是我目前的查询。

SELECT 
    `drawings`.`dwg_id`, 
    `project_no`, 
    `sws_dwg_no`, 
    `client_dwg_no`, 
    `dwg_title`, 
    `dwg_by`, 
    `dwg_rev`.`dwg_rev`, 
    `dwg_rev`.`dwg_date`, 
    MAX(`dwg_rev`.`dwg_rev`) AS dwg_rev 
FROM 
    (`drawings`) 
    JOIN `dwg_rev` ON `drawings`.`dwg_id` = `dwg_rev`.`dwg_id` 
WHERE 
    `project_no` = '153' 
GROUP BY 
    `sws_dwg_no`, 
    `dwg_rev`.`dwg_rev` 
ORDER BY 
    `dwg_rev`.`dwg_date` ASC, 
    `dwg_rev`.`dwg_rev` ASC

此查询返回的结果不包含最新的修订号，或者返回每个绘图的所有修订版。

Answer 1

您可以使用以下查询：

SELECT d.*, dr.*
FROM drawings AS d
INNER JOIN (
   SELECT dwg_id, MAX(rev_id) AS maxRevId
   FROM dwg_rev
   GROUP BY dwg_id
) AS t ON d.dwg_id = t.dwg_id   
INNER JOIN dwg_rev AS dr ON t.dwg_id = dr.dwg_id AND t.maxRevId = dr.rev_id
WHERE project_no = 153

上述查询的关键点是使用派生表返回最新版本，即MAX(rev_id)，每dwg_id。在该派生表上使用INNER JOIN，您可以从dwg_rev表中获取该行。

如果每dwg_id有多个 project_no，则必须使用上述内容。在这种情况下，上述查询将获取project_no = 153每张图纸的最新修订版。

Demo here

Answer 2

如果您需要最新版本，请订购以下DESC检查代码。

如果填充此rev_id，您也只能通过dwg_rev . rev_id` DESC进行订购。

SELECT附图. dwg_id , project_no , sws_dwg_no , client_dwg_no , dwg_title , dwg_by , dwg_rev . dwg_rev , dwg_rev . dwg_date , MAX( dwg_rev . dwg_rev ) AS dwg_rev FROM (附图) JOIN dwg_rev ON附图{ {1}} dwg_id . dwg_rev = dwg_id . project_no WHERE sws_dwg_no = '153' GROUP BY dwg_rev , dwg_rev . dwg_rev {{1 }} {dwg_date {1}} {dwg_rev {1}} {dwg_rev {1}}

Answer 3

有时MAX不是最佳方式，而是使用LIMIT试试这个：

SELECT 
    `drawings`.`dwg_id`, 
    `project_no`, 
    `sws_dwg_no`, 
    `client_dwg_no`, 
    `dwg_title`, 
    `dwg_by`, 
    `dwg_rev`.`dwg_rev`, 
    `dwg_rev`.`dwg_date`, 
    `dwg_rev`.`dwg_rev` AS dwg_rev 
FROM 
    (`drawings`) 
    JOIN `dwg_rev` ON `drawings`.`dwg_id` = `dwg_rev`.`dwg_id` 
WHERE 
    `project_no` = '153' 
GROUP BY 
    `sws_dwg_no`, 
    `dwg_rev`.`dwg_rev` 
ORDER BY 
    `dwg_rev`.`dwg_date` DESC, 
    `dwg_rev`.`dwg_rev` DESC
LIMIT 1;

连接2个表，只显示id的最大值 - mysql

3 个答案: