select c_gender 性别,COUNT(c_type) 总人数 from customers group by c_gender
4.统计order表中每一会员的订单总额，并显示大于平均总额的会员编号和订单总额
select c_id 会员编号,sum(o_sum) 订单总额 from orders group by c_id
having SUM(o_sum)>AVG(o_sum)
5.统计orders表中每一天的订单总额，并根据订单总额进行降序排序 select o_date,SUM(o_sum) 订单总额 from orders group by o_date
order by SUM(o_sum) desc
课堂实践4 p126
1.查询每笔订单的基本信息（订单号、订单日期、总金额）和付款方式以及处理该订单的员工名称 方法1：
select orders.o_id,o_date,o_sum,p_mode,employees.e_name from orders join payments