Question

所以我想要做的是，如果我的select中的结果与另一个post_id具有相同的post_data_id，则删除该结果但显示其中一个。我已经尝试了几天试图让这个工作，但失败了。请检查我的SQL Fiddle asweel作为我的意思的截图

由于

Answer 1

可能有一种更简单的方法，但您可以使用：

SELECT p.* 
FROM posts p 
LEFT JOIN following f 
    ON f.user_id=1 AND p.post_user_id = f.follower_id 
WHERE (post_user_id=1 
    OR f.follower_id IS NOT NULL) 
    AND (POST_DATA_ID NOT IN (SELECT POST_ID
                              FROM posts p 
                              LEFT JOIN following f 
                                  ON f.user_id=1 AND p.post_user_id = f.follower_id 
                              WHERE (post_user_id=1 
                                  OR f.follower_id IS NOT NULL))
        OR POST_DATA_ID IS NULL)
ORDER BY `post_id` DESC;

SQL Fiddle

Answer 2

您无法在一个语句中真正删除和 SELECT。您将始终需要连续执行两个语句。

我不确定您要删除哪些行（重复的post_id或重复的post_data_id），但您需要以下四个语句中的两个：

SELECT * FROM posts WHERE post_data_id IN (
SELECT post_id FROM posts);

SELECT * FROM posts WHERE post_id IN (
SELECT post_data_id FROM posts);

DELETE FROM posts WHERE post_data_id IN (
SELECT post_id FROM posts);

DELETE FROM posts WHERE post_id IN (
SELECT post_data_id FROM posts);

Answer 3

您可以使用NOT EXISTS并选择返回同一个表：

使用小提琴中的查询：

SELECT 
  p.* 
FROM
  posts p 
LEFT JOIN following f 
   ON f.user_id=1 AND p.post_user_id = f.follower_id 
WHERE 
  (post_user_id=1 
       OR f.follower_id IS NOT NULL) 
  and not exists (select 'x'
                from posts posts_2
               where p.post_data_id = posts_2.post_id)
ORDER BY `post_id` DESC

Answer 4

试试这个。我为group by添加了post_id，因为您希望该列是唯一的。我假设如果post_type相同，post_id等列值保证相同，因此您可以使用某些函数安全地聚合它们，例如MAX。

SELECT p.post_id, MAX(p.post_type), MAX(p.post_user_id), MAX(p.post_data_id) 
FROM posts p 
LEFT JOIN following f 
ON f.user_id=1 AND p.post_user_id = f.follower_id 
WHERE (post_user_id=1 
       OR f.follower_id IS NOT NULL) 
GROUP BY p.post_id
ORDER BY `post_id` DESC;

Answer 5

此查询存在相当多的问题，但我认为这个概念可能具有潜力：

SELECT -- p.* 
  GROUP_CONCAT(post_id) AS POST_IDs,
  GROUP_CONCAT(post_type) AS POST_TYPEs,
  GROUP_CONCAT(post_user_id) AS POST_USER_IDs,
  GROUP_CONCAT(post_data_id) AS POST_DATA_IDs
FROM posts p
LEFT JOIN following f
       ON p.post_user_id = f.follower_id 
WHERE 1 IN (p.post_user_id, f.user_id)
GROUP BY LEAST(POST_ID,COALESCE(POST_DATA_ID, POST_ID))
ORDER BY post_id DESC;

主要问题是知道在给定行中使用哪个POST_ID或POST_TYPE或POST_USER_ID。

Answer 6

这是获取指定结果的一种方法，使用原始查询作为内联视图。（实际上，查询引用了原始查询两次。我从原始查询中删除了ORDER BY。不需要删除它，但它也没有必要在那里。

SELECT a.*
  FROM (
         SELECT p.*
         FROM posts p
         LEFT JOIN following f
         ON f.user_id=1 AND p.post_user_id = f.follower_id
         WHERE (post_user_id=1
                OR f.follower_id IS NOT NULL)
       ) a
  LEFT
  JOIN (
         SELECT p.*
         FROM posts p
         LEFT JOIN following f
         ON f.user_id=1 AND p.post_user_id = f.follower_id
         WHERE (post_user_id=1
                OR f.follower_id IS NOT NULL)
       ) b
    ON b.post_id = a.post_data_id
 WHERE b.post_id IS NULL
 ORDER BY a.post_id DESC;

可能有更有效的方法来获得相同的结果，但此查询满足要求。它使用经典的angi-join模式：LEFT [OUTER] JOIN来查找匹配的行，并使用WHERE子句中的谓词来消除匹配的行。

e.g。从p获取行，其中q

中没有匹配的行

SELECT p.*
  FROM p
  LEFT
  JOIN q
    ON q.id = p.q_id
 WHERE q.id IS NULL

Answer 7

SELECT p.* 
FROM posts p 
LEFT JOIN following f 
ON f.user_id=1 AND p.post_user_id = f.follower_id 
LEFT JOIN post x
ON p.post_data_id=x.post_id
WHERE (p.post_user_id=1 
   OR f.follower_id IS NOT NULL) 
AND x.post_id is null
ORDER BY p.post_id DESC;

需要一些帮助隐藏结果MYSQL中的重复项

7 个答案: