分组数据

group by   创建分组   出现在where子句之后，order by子句之前

having

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

GROUP BY语句只是MYSQL按照vend_id排序并分组

排序和分组

mysql> select order_num,sum(quantity*item_price) as ordertotal from orderitems group by order_num having sum(quantity*item_price)>=50