mysql联合查询是什么

-- 示例：

select orders.order_id, orders.amt, customer.cust_name, customer.tel_no

from orders, customer

where orders.cust_id = customer.cust_id;

-- 起别名

select a.order_id, a.amt, b.cust_name, b.tel_no

from orders a, customer b

where a.cust_id = b.cust_id;