Question

我们假设我有两张桌子：人，车。 Table Car有一些列，其中一列是Human_id。例如，像这样：

Human_id Type
1        BMW
5        Mercedes
1        Audi
2        Peugeot
3        BMW
2        JEEP

如何选择所有拥有多辆车的人？我的意思是我需要控制在Human_id列中是否多次使用Human_id。但我怎么能这样做？

SELECT human.name
FROM Human, Car
WHERE .... <- what goes here??

Answer 1

尝试按Car对Human_id条记录进行分组，并查看HAVING条款。

Answer 2

SELECT human.name, car.human_id, count(*) as total
FROM Human, Car
group by human.name, car.human_id
having count(*) > 1

Answer 3

如果 Human 和 Car 表之间有FK，最好使用加入而不是笛卡尔积：

create table Human (
  idHuman integer primary key,
  name varchar(15),
   ...
);
insert into Human (idHuman, name) values
  (1,'A'), (2,'B'), (3,'C'), (4,'D'), (5,'E');

create table Car (
  Human_id integer REFERENCES Human ON DELETE CASCADE,
  Type varchar(15),
  ...
);
insert into Car (Human_id, Type) values 
  (1,'BMW'), (5,'Mercedes'), (1,'Audi')
 ,(2,'Peugeot'), (3,'BMW'), (2,'JEEP');

查询：

select hu.name
from Human hu
join Car ca on (ca.Human_id = hu.idHuman)
group by hu.name
having count(*) > 1

我希望我帮助你

Answer 4

 select human.name
 from human
 where human.id in
      select human.id
      from car
      where count(car) > 1
      group by human.id

postgres查询（超过函数）

4 个答案: