mysql - 内连接，右连接？计数行

Question

我如何发现哪些订单没有详细信息行？

Table Orders: orderId (int), customerName, deliveryDate (date), price (decimal)

Table Details: detailId (int), orderId (int), sku (varchar), quantity (int)

我试过了(没有成功):

SELECT
    COUNT(Details.detailId) AS Tot,
    Orders.orderId
FROM Details
INNER JOIN Orders
    ON Details.orderId = Orders.orderId
GROUP BY Details.orderId
HAVING Tot = 0

Answer 1

不在或不存在怎么样？

select o.*
from orders o
where not exists (select 1
                  from details d
                  where d.orderId = o.orderId
                 );

如果您不需要所有列，则在外部 select 中选择您想要的列。