join left join right join 关联问题

结果有15个

select p1.name ,p1.pricefrom product p1,product p2where p1.price = p2.price 

结果有8个

select p1.name ,p1.pricefrom product p1,product p2
where p1.price = p2.Price and p1.name <> p2.name

结果5个

select p1.name ,p1.pricefrom product p1,product p2
where p1.price =p2.Price and p1.name<> p2.name
group by   p1.name ,p1.price

–	–