为每个 SID 删除除 2 行以外的所有行（降序）

Question

我有一个 table 这种结构。每个 SID 都有不同的 ITEMID

| sid | itemid |
|---| ---------|
| 1 | 20600    |
| 1 | 20598    |
| 1 | 20597    |
| 1 | 20596    |
| 1 | 20595    |
| 1 | 20594    |
...
...
| 2 | 19600    |
| 2 | 19598    |
| 2 | 19597    |
| 2 | 19596    |
| 2 | 19595    |
| 2 | 19594    |
...
...

我需要的是删除除最后 2 行之外的所有 ITEMID 以降序方式排序的行。这是我想要得到的结果：

| sid | itemid |
|---| ---------|
| 1 | 20600    |
| 1 | 20598    |
| 2 | 19600    |
| 2 | 19598    |

谢谢安德里亚

Answer 1

在 MySQL 8+ 上，我们可以尝试使用 ROW_NUMBER:

删除连接

DELETE t1
FROM yourTable t1
INNER JOIN
(
    SELECT sid, itemid,
           ROW_NUMBER() OVER (PARTITION BY sid ORDER BY itemid DESC) rn
    FROM yourTable
) t2
    ON t2.sid = t1.sid AND t2.itemid = t1.itemid
WHERE
    t2.rn > 2;

Answer 2

DELETE t0
FROM test t0
JOIN ( SELECT t1.sid,
              ( SELECT itemid
                FROM test t2
                WHERE t1.sid = t2.sid
                ORDER BY itemid DESC LIMIT 1,1 ) itemid
       FROM ( SELECT DISTINCT t3.sid
              FROM test t3 ) t1 ) t4 USING (sid)
WHERE t0.itemid < t4.itemid;

https://dbfiddle.uk/?rdbms=mysql_5.5&fiddle=c6d67da817ddbb9fb890693564bcd49c

为每个 SID 删除除 2 行以外的所有行（降序）

Delete all rows except 2 for each SID (descending order)

mysql

mysql-5.5

sql-delete