sql语言

select *from customers

 

select *from orders

 

select customers.cust_id, orders.order_num  from customers inner join orders on customers.cust_id=orders.cust_id

 

select customers.cust_id, orders.order_num  from customers left outer join orders on customers.cust_id=orders.cust_id

 使用带聚集函数的连接

select customers.cust_id,count(orders.order_num) as num_ord from customers inner join orders on customers.cust_id = orders.cust_id group by customers.cust_id

 

select customers.cust_id,count(orders.order_num) as num_ord from customers left outer join orders on customers.cust_id = orders.cust_id group by customers.cust_id