如何修改此工作 SQL SELECT/JOIN 查询以删除重复项？

Posted 2023-02-24

【中文标题】如何修改此工作 SQL SELECT/JOIN 查询以删除重复项？

【英文标题】：How to modify this working SQL SELECT/JOIN query to DELETE the duplicates?

【发布时间】：2015-10-04 20:48:56

【问题描述】：

我无法修改它以删除重复记录。在这种情况下，对于给定的 meta_key，我有三个具有相同 meta_value 的帖子，它返回了两个结果（我可能对 GROUP BY 有问题——仍在解决它）。但是，将第一个 SELECT 更改为 DELETE 不起作用。这不是我要更改的部分，以便从两个表中删除数据吗？

$sql1 = "SELECT * 
         FROM (
             SELECT wp_posts.ID, wp_posts.post_title, wp_posts.post_type, wp_posts.post_status, wp_postmeta.meta_value 
             FROM wp_posts, wp_postmeta 
             WHERE wp_posts.ID=wp_postmeta.post_ID 
             AND post_type='banners' 
             AND post_status='publish' 
             AND meta_key='uselink' 
             AND meta_value='http://www.mylink.com/subpage/') 
         AS a 
         INNER JOIN ( 
             SELECT meta_value, MIN( post_id ) 
             AS min_id 
             FROM wp_postmeta 
             GROUP BY meta_value 
             HAVING COUNT( * ) > 1  ) 
         AS b 
         ON b.meta_value = a.meta_value 
         AND b.min_id <> a.id";

$result1 = $conn->query($sql1);

if ($result1->num_rows > 0) 
    while($row = $result1->fetch_assoc()) 
        echo $row["meta_value"] . ", ";
    
 else 
    echo "0 results";

这是我尝试过的（不工作）：

$sql1 = "DELETE * 
         FROM (
             SELECT wp_posts.ID, wp_posts.post_title, wp_posts.post_type, wp_posts.post_status, wp_postmeta.meta_value 
             FROM wp_posts, wp_postmeta 
             WHERE wp_posts.ID=wp_postmeta.post_ID 
             AND post_type='banners' 
             AND post_status='publish' 
             AND meta_key='uselink' 
             AND meta_value='http://www.mylink.com/subpage/') 
        AS a 
        INNER JOIN ( 
             SELECT meta_value, MIN( post_id ) 
             AS min_id FROM wp_postmeta 
             GROUP BY meta_value HAVING COUNT( * ) > 1  ) 
        AS b 
        ON b.meta_value = a.meta_value 
        AND b.min_id <> a.id";

在没有第二个可用的连接表的情况下，我将关闭这个：

DELETE a.* 
FROM wp_posts 
AS a 
INNER JOIN ( 
    SELECT post_title, MIN( id ) 
    AS min_id 
    FROM wp_posts 
    WHERE post_type = 'banners' 
    AND post_status = 'publish' 
    GROUP BY post_title HAVING COUNT( * ) > 1  ) 
AS b 
ON b.post_title = a.post_title AND b.min_id <> a.id 
AND a.post_type = 'banners' 
AND a.post_status = 'publish'

【问题讨论】：

select 和 delete 查询的区别是 SELECT * FROM table WHERE this=that 和 Delete FROM table WHERE this=that，所以你看到用 select 替换 just delete 是行不通的

我添加了这个问题只是为了帮助我把它放在我的脑海里。我只是不清楚如何处理，因为只有一个表只是将第一个 SELECT 更改为 DELETE 确实有效；不知道是不是跟有两张表有关？

我加入表格后是否需要删除？是这个问题吗？

首先你必须从 DELETE QUERY 中删除 *，它应该看起来像 DELETE FROM 而不是 DELETE * FROM 第二你不能在 InnerJoin 中选择，只需使用 WHERE 子句加入表格即可去

SQL DELETE with INNER JOIN 的可能重复项

【参考方案1】：

试试这个，（但我不确定）

$sql1 = "DELETE p, pm
FROM wp_posts p
INNER JOIN wp_postmeta pm ON p.ID=pm.post_ID
WHERE p.post_type='banners'
AND p.post_status='publish'
AND pm.meta_key='uselink'
AND pm.meta_value='link'
AND (SELECT count(pm.meta_value) FROM
wp_postmeta pm
GROUP BY pm.meta_value
HAVING COUNT(*) > 1
WHERE pm.meta_value=p.meta_value)";

【讨论】：

感谢您的跟进；我可以遵循我认为的那种逻辑。我一定是误会了重复计数检查。我想查找并删除那些重复项。选择返回了它们，但我就是不知道如何整合 INNER JOIN/HAVING COUNT 部分

例如，对于我一直在尝试的所有不同迭代，这确实会根据 WHERE 条件删除帖子，但现在我只需要删除重复项：$sql1 = "DELETE p, pm FROM wp_posts p INNER JOIN wp_postmeta pm ON p.ID=pm.post_ID WHERE p.post_type='banners' AND p.post_status='publish' AND pm.meta_key='uselink' AND pm.meta_value='mylink.com/subpage'";

很抱歉没有回来查看；我仍在努力... 5 天，数...谢谢您的指导 - 必须接近