USE northwindSELECT *
FROM orders AS or1
WHERE 20 <
( SELECT quantity
FROM [order details] AS od
WHERE or1.orderid = od.orderid
AND od.productid = 23
)想知道 ( SELECT quantity FROM [order details] AS od WHERE or1.orderid = od.orderid AND od.productid = 23)里面得到的是什么? 不是满足条件的quantity字段吗? 如果是 在表orders里面并没有这个字段,为什么依然可以查出结果?新手问题 高手不要鄙视
FROM [order details] AS od
WHERE or1.orderid = od.orderid
AND od.productid = 23
)这只有一条满足么,多条的时候会有问题的
FROM [order details] AS od
WHERE or1.orderid = od.orderid
AND od.productid = 23
查出来的是满足条件的数据集合,然后外层的是满足条件quantity>20的数据
USE northwindSELECT *
FROM orders AS or1, order daetails as od
where or1.orderid=od.orderid and od.productid=23 and od.quantity>20
order details 表里面满足条件的数据吗?
如果是 那满足外层条件以后不是也应该返回了
order details 表里面满足条件的数据吗?--没读懂什么意思,order details 表里的结果集只作为orders 表的条件