聚合函数不能在where子句使用

1、查询出销售表中，销售额大于本地区平均水平的记录，用一条SQL语句

--创建sales表

create table sales( OrderID int,Region char(1),Total float )

--向表中插入数据

insert into sales

select '2','C',80.00 union

select '3','A',130.00 union

select '4','B',90.00 union

select '6',120.00 union

select '7',90.00 union

select '9',80.00 union

select '1',100.00 union

select '5',100.00 union

select '8',90.00

--容易出现的错误例子：

select *

from sales

where total>sum(total)/count(1)

group by region

--正确的查询：

select a.* from sales a,(select region,sum(total)/count(1) as av from sales group by region) b

where a.region=b.region and a.total>b.av