问题描述
我正在尝试让 sql 删除所有重复的标题但必须在以下条件下删除重复的标题:
I'm trying to make sql who will delete all duplicate titles BUT must delete duplicates with these conditions:
- 必须只删除具有相同 object_id 的重复项
- 必须只保留最新的记录(最大的topic_id)(topic_id 是每个主题 AI 的唯一 id)
- must delete only duplicates with same object_id
- must keep only the newest record (biggest topic_id) (topic_id is the unique id for every topic AI)
到目前为止，我已经完成了(使用 select... 进行测试)
So far I've done that (testing with select...)
SELECT topic_id,object_id,title,url,date
FROM topics GROUP BY title
HAVING ( COUNT(title) > 1)
ORDER BY topic_id DESC
但不符合条件.
我正在使用 mysql.
But doesn't meet the conditions.
I'm using mysql.
推荐答案
在 MySQL 中，不能将目标表指定给子查询中的 DML 操作(除非您将其嵌套不止一层，但在这种情况下，您将无法获得可靠的结果，也无法使用相关的子查询).
In MySQL, you cannot specify the target table to a DML operation in a subquery (unless you nest it more than one level deep, but in this case you won't get reliable results and cannot use correlated subqueries).
使用 JOIN:
DELETE td
FROM topics td
JOIN topics ti
ON ti.object_id = td.object_id
AND ti.title = td.title
AND ti.topic_id > td.topic_id;
在 topics (object_id, title, topic_id) 上创建索引，以便快速工作.
Create an index on topics (object_id, title, topic_id) for this to work fast.
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