Mysql基础第十七天,使用子查询

Posted 2021-08-03 2019ab

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子查询

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

利用子查询进行过滤

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

作为计算字段使用子查询

  select cust_name,(select count(*) from orders where cust_id = customers.cust_id) as num_orders from customers;

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