删除除具有最大值的行之外的所有行

Posted 2023-05-08

【中文标题】删除除具有最大值的行之外的所有行

【英文标题】：Delete all rows except the one with the biggest value

【发布时间】：2016-04-08 16:11:17

【问题描述】：

我将交易存储在一个表中，我想删除所有交易（按 user_id 分组），除了金额最大的交易，这里是一个示例表：

+----+---------+--------+
| id | user_id | amount |
+----+---------+--------+
| 1  | 1       | 10     |
+----+---------+--------+
| 2  | 1       | 20     |
+----+---------+--------+
| 3  | 1       | 30     |
+----+---------+--------+
| 4  | 2       | 50     |
+----+---------+--------+
| 5  | 2       | 100    |
+----+---------+--------+
| 6  | 3       | 2      |
+----+---------+--------+
| 7  | 3       | 4      |
+----+---------+--------+

我想要以下结果

+----+---------+--------+
| id | user_id | amount |
+----+---------+--------+
| 3  | 1       | 30     |
+----+---------+--------+
| 5  | 2       | 100    |
+----+---------+--------+
| 7  | 3       | 4      |
+----+---------+--------+

我试过了

DELETE FROM `transactions`
WHERE `user_id` NOT IN (
  SELECT `user_id`
  FROM (
    SELECT MAX(`amount`) AS ts
    FROM `transactions` e
    WHERE `user_id` = `user_id`
  ) s
  WHERE ts = `transactions`.`amount`
)
ORDER BY `transactions`.`user_id` ASC

【问题讨论】：

How to delete duplicates on a mysql table?的可能重复

也许用删除的标志更新而不是删除它们。

@Gerfried 我不想删除重复值，我想删除除较大金额之外的所有值示例：用户有 4 笔交易，1- 10 美元 2- 20 美元 3- 40 美元我想删除 1 和 2 并保留 40 美元

【参考方案1】：

DELETE FROM `transactions`
WHERE id NOT IN 
(
    SELECT MAX(id)
    FROM `transactions`
    group by user_id
)

每个用户的内部查询组，并且只为每个用户选择最高 ID。从内部选择中删除除 ID 之外的所有记录。

【参考方案2】：

不确定except the latest one 是什么意思，所以我考虑了except last record inserted，因此使用了ORDER BY id DESC

DELETE FROM `transactions`
WHERE `id` NOT IN (
    SELECT `id`
    FROM `transactions`
    GROUP BY `user_id`
    ORDER BY `id` DESC
)