删除在 MySQL 表列中出现最多 2 次的所有重复项之一

Question

我有一个大约 10,000 条记录的表，其中标题中有重复项，有些重复超过 5 次。

样本数据

id| titleslug | views
--------------------
1 |the-box|  200
2 |the-box|  100
3 |the-box|   10
4 |the-man|   15
5 |the-man|   30
6 |the-cup|   10
7 |the-cup|   20

该框出现了 3 次，所以我想留下它，但 'the-man' 和 'the-cup' 出现了 2x 我想删除它们中的每一个，以便决赛桌变成

id| titleslug | views
--------------------
1 |the-box|  200
2 |the-box|  100
3 |the-box|   10
5 |the-man|   30
7 |the-cup|   20

如果可能的话，我想将被删除的观看次数添加到保留的最高观看次数中。

通过下面的查询，我能够知道项目重复的次数。

select titleslug, count(*) as c from articles
group by titleslug having c > 1
order by c desc

我想删除仅重复两次的记录之一，并保留其余记录。 我正在考虑这个查询如下

 DELETE a
    FROM articles as a, articles as b
    WHERE
     (a.titleslug = b.titleslug OR a.titleslug IS NULL AND b.titleslug IS NULL)
      AND a.views < b.views;

但我需要帮助来限制仅当我们有两个重复项时才删除一个。

我使用了下面的查询，它报告了受影响的行，但是在我查询之后似乎没有删除重复项

DELETE a
  FROM articles_copy a
  JOIN (SELECT MAX(t.Views) AS max_a1, t.TitleSlug
          FROM articles_copy t
      GROUP BY t.TitleSlug, t.Views
        HAVING COUNT(*)>1 AND COUNT(*)<=2) b ON b.TitleSlug = a.TitleSlug
                              AND b.max_a1 > a.View

Answer 1

一个选项可以是（评估性能问题）：

mysql> DROP TABLE IF EXISTS `articles`;
Query OK, 0 rows affected (0.00 sec)

mysql> CREATE TABLE IF NOT EXISTS `articles` (
    ->   `id` INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
    ->   `title` VARCHAR(25) NOT NULL,
    ->   `views` INT UNSIGNED
    -> );
Query OK, 0 rows affected (0.00 sec)

mysql> INSERT INTO `articles`
    ->   (`title`, `views`)
    -> VALUES
    ->   ('the-box', 200),
    ->   ('the-box', 100),
    ->   ('the-box', 10),
    ->   ('the-man', 15),
    ->   ('the-man', 30),
    ->   ('the-cup', 10),
    ->   ('the-cup', 20);
Query OK, 7 rows affected (0.00 sec)
Records: 7  Duplicates: 0  Warnings: 0

mysql> SELECT
    ->   `id`,
    ->   `title`,
    ->   `views`
    -> FROM
    ->   `articles`;
+----+---------+-------+
| id | title   | views |
+----+---------+-------+
|  1 | the-box |   200 |
|  2 | the-box |   100 |
|  3 | the-box |    10 |
|  4 | the-man |    15 |
|  5 | the-man |    30 |
|  6 | the-cup |    10 |
|  7 | the-cup |    20 |
+----+---------+-------+
7 rows in set (0.00 sec)

mysql> START TRANSACTION;
Query OK, 0 rows affected (0.00 sec)

mysql> UPDATE `articles`
    ->   INNER JOIN (
    ->     SELECT MAX(`id`) `id`, SUM(`views`) `views`
    ->     FROM `articles`
    ->     GROUP BY `title`
    ->     HAVING COUNT(`title`) = 2
    ->   ) `der`
    -> SET `articles`.`views` = `der`.`views`
    -> WHERE `articles`.`id` = `der`.`id`;
Query OK, 2 rows affected (0.00 sec)
Rows matched: 2  Changed: 2  Warnings: 0

mysql> DELETE FROM `articles`
    -> WHERE `id` IN (SELECT MIN(`der`.`id`)
    ->                FROM (SELECT `id`, `title`
    ->                      FROM `articles`) `der`
    ->                GROUP BY `der`.`title`
    ->                HAVING COUNT(`der`.`title`) = 2);
Query OK, 2 rows affected (0.00 sec)

mysql> COMMIT;
Query OK, 0 rows affected (0.00 sec)

mysql> SELECT
    ->   `id`,
    ->   `title`,
    ->   `views`
    -> FROM
    ->   `articles`;
+----+---------+-------+
| id | title   | views |
+----+---------+-------+
|  1 | the-box |   200 |
|  2 | the-box |   100 |
|  3 | the-box |    10 |
|  5 | the-man |    45 |
|  7 | the-cup |    30 |
+----+---------+-------+
5 rows in set (0.00 sec)