如果按列计数大于1，如何删除特定列中值最小的行答案

【问题标题】：How to delete the row that has least value in a specific column if group by count of the column is greater than 1如果按列计数大于1，如何删除特定列中值最小的行
【发布时间】：2020-12-06 19:41:54
【问题描述】：

我有一张如下表所示的名称推荐

我想删除cnt具有最小值且存在ID_recipient多条记录的所有行。

如果有 ID_recipient 的单个记录，则无论 cnt 的值可能是什么，它都不应该被删除。

以蓝色突出显示的是必须保留的记录。

我试过了：

DELETE from table where( 
    SELECT DISTINCT(A.ID_recipient), DISTINCT(A.cnt) FROM (
          SELECT  MIN(cnt) as cnt FROM recomendation_table_ID_recipient GROUP BY ID_recipient HAVING COUNT(*) > 1 ) as A);

这不起作用。

【问题讨论】：

请参阅Why should I provide an MCRE for what seems to me to be a very simple SQL query，并注意 DISTINCT 不是函数。
我用一些测试数据创建了一个 db-fiddle，但正如@Strawberry 指出的那样，如果您希望将来获得帮助，您应该这样做。
我相信你下次也可以为 OP 做这一切。

标签： mysql sql duplicates sql-delete

【解决方案1】：

如果你想使用二维，你必须使用 IN 子句。

你的子查询没有多大意义，所以你应该先测试一下，或者用想要的例子发布数据

DELETE from recomendation_table_ID_recipient where (ID_recipient,cnt) IN ( 
    SELECT DISTINCT A.ID_recipient, A.cnt FROM (
          SELECT ID_recipient, MIN(cnt) as cnt FROM recomendation_table_ID_recipient GROUP BY ID_recipient HAVING COUNT(*) > 1 ) as A);

【讨论】：

【解决方案2】：

delete t1 from recomendation_table_ID_recipient t1 join (
    select ID_recipient, min(cnt) as cnt from recomendation_table_ID_recipient
    group by ID_recipient
    having count(*) > 1
) t2 on t1.ID_recipient = t2.ID_recipient and t1.cnt = t2.cnt;

See db-fiddle

【讨论】：