SQL语句练习实例之三——平均销售等待时间

复制代码 代码如下:

—1.平均销售等待时间

—有一张sales表，其中有销售日期与顾客两列，现在要求使用一条sql语句实现计算

–每个顾客的两次购买之间的平均天数

–假设：在同一个人在一天中不会购买两次

create table sales

(

custname varchar(10) not null,

saledate datetime not null

)

go

insert sales

select ‘张三’,’2010-1-1′ union

select ‘张三’,’2010-11-1′ union

select ‘张三’,’2011-1-1′ union

select ‘王五’,’2010-2-1′ union

select ‘王五’,’2010-4-1′ union

select ‘李四’,’2010-1-1′ union

select ‘李四’,’2010-5-1′ union

select ‘李四’,’2010-9-1′ union

select ‘李四’,’2011-1-1′ union

select ‘赵六’,’2010-1-1′ union

select ‘钱途’,’2010-1-1′ union

select ‘钱途’,’2011-3-1′ union

select ‘张三’,’2011-9-1′

go

select custname,datediff(d,min(saledate),max(saledate))/(count(*)-1) as avgday

from sales

group by custname

having count(*)>1

go

select custname,case when count(*)>1 then datediff(d,min(saledate),max(saledate))/(count(*)-1)

else datediff(d,min(saledate),max(saledate)) end

as avgday

from sales

group by custname

–having count(*)>1

go

drop table sales