Question

我和the one solved here有类似的问题，但是当我尝试解决方案时，我认为它失败了，因为我的设置不同......

我有一张doc表... （遗憾的是，由于它是旧系统，因此无法编辑表格）

+-------+--------+----------+--------+
| Docid | title  | revision | linkid |
+-------+--------+----------+--------+
| 1     | docone | 1        | 1      |
| 2     | doctwo | 1        | 2      |
| 3     | docone | 2        | 1      |
|4      | docone | 3        | 1      |
+-------+--------+----------+--------+

在列出所有文档的页面上，我只想列出每个文档的最新版本。例如，Doc1在修订版3上，所以我想要那个而不是其他2. Doc2只在修订版1上，所以显示一个。

基于另一篇文章中的问题，我将查询写成如下......

$query_docs = "
    SELECT `document`.*, doctype.* 
    FROM `document`   
    INNER JOIN doctype    
        ON `document`.iddoctypes = doctype.iddoctypes
    WHERE `document`.revision = (
        SELECT MAX(`document`.revision) AS revision 
        FROM `document`
    )  
    GROUP BY `document`.linkid   
    ORDER BY `document`.doccreation DESC";

我不得不链接到另一个表来获取文档类型（只是为了使查询更难）。

Answer 1

只是猜测：我认为您必须在group by title子查询中添加(select max(...) ...)。

所以完整的陈述将是：

$query_docs = "
SELECT `document`.*, doctype.* 
FROM `document`   
INNER JOIN doctype    
    ON `document`.iddoctypes = doctype.iddoctypes
WHERE `document`.revision = (
    SELECT MAX(`document`.revision) AS revision 
    FROM `document`
    --GROUP BY `document`.title
    GROUP BY `document`.linkid
)  
GROUP BY `document`.linkid   
ORDER BY `document`.doccreation DESC";

Answer 2

试试这个，我做了一些小改动

SELECT document.*, doctype.* 
FROM document   
INNER JOIN doctype    
    ON document.iddoctypes = doctype.iddoctypes
WHERE document.revision = (
    SELECT MAX(d1.revision)
    FROM document d1 
    WHERE document.linkid = d1.linkid
)  
ORDER BY document.doccreation DESC

Answer 3

我错过了什么吗？这似乎完全是直截了当的......

SELECT x.*
  FROM my_table x
  JOIN (SELECT title,MAX(revision) max_revision FROM my_table GROUP BY title) y
    ON y.title = x.title 
   AND y.max_revision = x.revision;

找到列的最大值，然后按同一表中的另一列进行分组

3 个答案: