如何根据字段值对行进行分组？也许是一个 RANK() 案例？

Question

对于不好的实现，我们有这样的情况：

+-----------+-------- +-----------+-----------+-----------+---------+------------------------+---------------------+---------------------+-----------+----------+---------+--------
| id        | event_n | reader_id | entity_id | school_id | root_id | event_value            | created_at          | updated_at          | event_flo | event_int| user_id | teacher
+-----------+-------- +-----------+-----------+-----------+---------+------------------------+---------------------+---------------------+-----------+----------+---------+--------
| 345678270 | search  | 2511678   | 193765    | <null>    | 65478   | Du mmy                 | 2021-04-05 19:24:11 | 2021-04-05 19:24:11 | <null>    | <null>   | 2634876 | <null> 
| 345678286 | search  | 2511678   | 193765    | <null>    | 65478   | Du mmyntex             | 2021-04-05 19:24:13 | 2021-04-05 19:24:13 | <null>    | <null>   | 2634876 | <null> 
| 345678366 | search  | 2511678   | 193765    | <null>    | 65478   | Du mmyntexas           | 2021-04-05 19:24:17 | 2021-04-05 19:24:17 | <null>    | <null>   | 2634876 | <null> 
| 345678370 | search  | 2511678   | 193765    | <null>    | 65478   | Du mmyntexas de ma     | 2021-04-05 19:24:17 | 2021-04-05 19:24:17 | <null>    | <null>   | 2634876 | <null> 
| 345678388 | search  | 2511678   | 193765    | <null>    | 65478   | Du mmyntexas de make   | 2021-04-05 19:24:18 | 2021-04-05 19:24:18 | <null>    | <null>   | 2634876 | <null> 
| 345678823 | search  | 2587432   | 61567     | <null>    | 65478   | du mmyntexas do clock  | 2021-04-05 19:24:52 | 2021-04-05 19:24:52 | <null>    | <null>   | 2713377 | <null> 
| 345678315 | search  | 2511678   | 193765    | <null>    | 65478   | Du mmyntexasd          | 2021-04-05 19:24:14 | 2021-04-05 19:24:14 | <null>    | <null>   | 2634876 | <null>

应该只记录较长的 event_value 列。我们已经解决了这个问题。但是，任何人都可以看到按这些寄存器分组的方法，所以我可以删除它们，只留下最大的长度？

我考虑过使用 RANK() 函数，但找不到对这些值进行分组的方法。

Answer 1

类似

DELETE t1
FROM tablename t1
JOIN tablename t2 
    -- adjust joining columns list
    USING (event_n, reader_id, entity_id, user_id)
WHERE LOCATE(t1.event_value, t2.event_value) = 1
  AND t1.created_at < t2.created_at
  -- adjust time gap length
  AND t1.created_at + INTERVAL 1 MINUTE > t2.created_at

或使用 WHERE EXISTS 相同。

如何根据字段值对行进行分组？也许是一个 RANK() 案例？

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