分组数据

指定分组后，对每个分组里的数据进行聚集

1. select vend_id, count(*) as num_prods from products group by vend_id;

2. 过滤分组
   select cust_id, count(*) from orders group by cust_id having count(*) > =2;

注意： where是在分组前进行过滤，having是在分组后进行过滤

1. 价格>=10, 具有2个产品及其以上的供应商。
   select vend_id, count(*) as num_prods from products where prod_price >=10 group by vend_id having count(*) >=2;

2. 总计订单价格大于等于50的订单号和总计价格
   select order_num, sum(quantity * item_price) as ordertotal from orderitems group by order_num having sum(quantity * item_price) >=50;

3. select order_num, sum(quantity * item_price) as ordertotal from orderitems group by order_num having sum(quantity * item_price) >=50 order by ordertatal