SELECT productNo ,count(quantity ) 销售数量,avg(price ) 平均销售单价,sum(quantity *price ) 总销售额
FROM OrderDetail GROUP BY productNo ORDER BY productNo 结果：
(13) 查找至少有3次销售的业务员名单和销售日期。 命令：
SELECT employeeName ,orderDate FROM Employee a,OrderMaster b,( SELECT salerNo FROM OrderMaster GROUP BY salerNo HAVING count(*)>=3) c
WHERE employeeNo =b.salerNo and b.salerNo =c.salerNo GROUP BY employeeName ,orderDate 结果：
(14) 用存在量词查找没有订货记录的客户名称。 命令：
SELECT CustomerName FROM Customer a WHERE NOT EXISTS ( SELECT CustomerNo FROM OrderMaster b WHERE a.CustomerNo =b.CustomerNo )