SELECT cust_name,
cust_state,
(SELECT COUNT(*)
FROM orders
WHERE oders.cust_id = customers.cust_id) AS orders
FROM customers
ORDER BY cust_name;
上面得SOL会返回customers表中的每个行,和他们在order表中出现的次数。
书上说:子查询总是从内向外处理。
但是 SELECT COUNT(*)
FROM orders,customers
WHERE oders.cust_id = customers.cust_id)
只会返回一行就是表中的行数!怀疑从内向外执行!求解!
FROM orders
WHERE oders.cust_id = customers.cust_id) AS orders并不等同于 SELECT COUNT(*)
FROM orders,customers
WHERE oders.cust_id = customers.cust_id) 什么书上讲的?上下文是什么?你是如何理解的?
入门级的书,讲子查询的!
ACMAIN仁兄 你回复的太快了!
既然ACMAIN_CHM老大推荐,去书店的时候看看!找一本好教材是一项hardwork!