具有聚合函数SQL的子查询

Question

目标是更新Inventory表的object_category列，用于表中项目数量最少的对象（count（name））

我知道在为子句使用子查询时，子查询必须返回单个列或值。但是，我不确定如何在保持语法正确的同时实现我的目标。

这是我到目前为止的代码，子查询本身产生了正确的两个要更新的对象，而不是当我把它放在IN子句中时

UPDATE Inventory
SET object_category = 'ABC'
WHERE Inventory.object_category in (
select count(name) as nameCount , object_category
from Inventory
group by object_category
having nameCount <= min(nameCount));

Answer 1

在MySQL中，您需要使用join表达此逻辑。如果您只想更新一个类别，那么这就足够了

UPDATE Inventory i JOIN
       (SELECT count(name) as nameCount, object_category
        FROM Inventory
        GROUP BY object_category
        ORDER BY nameCount
        LIMIT 1
       ) ii
       ON ii.object_category = i.object_category
    SET i.object_category = 'ABC';

您的子查询没有意义，也不起作用。