问题描述

我在我的表中发现了需要删除的重复项.该表包含:

I found duplicates in my table which needed to be removed. The table contains:

1. ID - 表的唯一键
2. STUDENT_ID - 学生的 ID
3. SUBJECT_ID - 学生的科目
4. CLASS_ID - 班级学生在
5. XP_LVL - 专业水平

一个学生应该只有一个科目、班级和 XP_lvl 的记录.在这种情况下，删除重复项是基于删除所有但保留一个.

One student should have only one record of subject, class and XP_lvl. In this case the removal of duplicities is based on delete all but keep one.

在我的情况下，重复看起来像这样:

In my case duplicates looks like this:

我通过创建 (CONCAT(STUDENT_ID, CONCAT(SUBJECT_ID, CLASS_ID))) 的唯一 ID，然后通过 count.. >1 识别出所有重复项> 工作正常.

I have identified all the duplicates by creating unique ID of (CONCAT(STUDENT_ID, CONCAT(SUBJECT_ID, CLASS_ID))) and then by having count.. >1 which works fine.

现在我需要识别所有 ID，以便我可以在从查询中删除时使用 ID NOT IN (SELECT...).

Now I need to identify all the ID so I can use ID NOT IN (SELECT...) in my delete from query.

所以我这样做了..

AND ID NOT IN (SELECT UID FROM (
SELECT
    min(ID) AS UID,
    STUDENT_ID,
    SUBJECT_ID,
    CLASS_ID    
FROM
    my_table 
GROUP BY
    STUDENT_ID,
    SUBJECT_ID,
    CLASS_ID    
HAVING
    count(CONCAT(STUDENT_ID, CONCAT(SUBJECT_ID, CLASS_ID))) > 1))

但是，我不能使用 min/max(ID) 来选择要保留的 ID，因为正如您所见，对于学生 2AAB，存在具有不同 XP_LVL 的重复项.

However I cannot use min/max(ID) to choose which ID to keep because as you can see for student 2AAB there are duplicities with different XP_LVL.

在这种情况下，我需要选择最高 XP_LVL 的 ID 来保留和删除所有其他的.

In this case I need to select ID of highest XP_LVL to keep and delete all other.

我尝试使用 RANK、ROWNUM 不同的排序和子选择的负载，但没有想要的结果.

I tried using RANK, ROWNUM different ordering and loaaads of subselects but without desired results.

有谁知道如何有效地做到这一点?我们正在谈论 6k 重复，所以我不能一一做.提前感谢您的帮助.

Does anyone have any idea how to do it effectively ? We are talking about 6k duplicities so I cant do it one by one. Thank you for your help in advance.

推荐答案

您可以使用 ROW_NUMBER 解析函数并使用 ROWID 伪列关联删除:

You can use ROW_NUMBER analytic function and correlate the deletion using the ROWID pseudo-column:

DELETE FROM my_table
WHERE ROWID IN (
  SELECT ROWID
  FROM   (
    SELECT ROW_NUMBER() OVER (
             PARTITION BY student_id, subject_id, class_id
             ORDER BY expertise_lvl DESC
           ) AS rn
    FROM   my_table
  )
  WHERE  rn > 1
)

db<>fiddle 这里

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