MySql 子查询

使用子查询进行过滤

举例：

select cust_name, cust_contact
from customers
where cust_id in (select cust_id
             from orders
             where order_num in (select order_num
                           from orderitems
                           where prod_id='TNT2'));
                           

说明：列出订购物品TNT2的所有客户

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作为计算字段使用子查询

select cust_name,
     cust_state,
     (select count(*)
      from orders
      where orders.cust_id = customers.cust_id) as orders
from customer
order by cust_name;

说明：显示customer表中每个客户的订单总数

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注意：上面给出的样例代码运行良好，但它并不是解决这种数据检索的最有效的方法

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参考书籍：

• MySQL必知必会