高级非重复SQL查询有问题

这似乎至少在SQL Server中有效:

select  product_id
from    (
            select product_id,
                   sum((case when action='add' then 1 else -1 end)) as number
            from   bills_products
            group by product_id
        ) as counts
where   number > 0

SELECT DISTINCT product_id FROM bills_products WHERE action = 'add';

GSTO差点就拿到了,但你必须 ORDER BY bill_id DESC 以确保您获得最新的记录。

SELECT DISTINCT product_id FROM bills_products
WHERE action = 'add'
ORDER BY bill_id DESC;

(P.S.我认为大多数人都会说,在这样的表上有一个时间戳列是一种最佳实践,您需要知道“最新”行是什么。您不能总是只依赖ID升序。)