Question

我有以下两个表：

People [*ID*, Name] 
Pet [*PetID*, OwnerID, Species, Name]

（OwnerID是ID的外键）

我希望数据库列出每个人以及他们拥有的不同种类的数量。例如，如果Bob（ID 1473）拥有狗，猫和另一只狗，则输出应为：

ID    | No. of Species
----------------------
1473  | 2

我意识到这需要相关的子查询或外连接，但我不确定如何做到这一点。任何帮助将不胜感激。

Answer 1

您可以使用count(distinct ...)：

select  People.ID
,       count(distinct Species)
from    People
join    Pet
on      Pet.OwnerID = People.ID
group by
        People.ID

Answer 2

试试这个

Select ID,[No. of Species] from People 
inner join 
  ( select Count(Species) as [No. of Species],OwnerID from Pet  
   group by OwnerID) d 
on Id = d.OwnerID

Answer 3

select people.name, count(distinct pet.species)
from people, pet
where people.id = pet.ownerid
group by people.name

SQL查询 - 结果不同

3 个答案: