在postgres

Question

我有下表

|------------------------|
| owner | animal | color |
|------------------------|
| John  | dog    | black |
| Peter | dog    | brown |
| John  | cat    | green |
| Lisa  | dog    | white |
| Peter | cat    | black |
|------------------------|

我需要归还哪位老板有黑狗和绿猫，结果必须是'John'

我试了这个没有运气

SELECT owner FROM pets
WHERE 
(
EXISTS ( SELECT * FROM pets WHERE animal = 'dog' AND color = 'black' ) 
AND 
EXISTS ( SELECT * FROM pets WHERE animal = 'cat' AND color = 'green' )
)

Answer 1

选择那些与其中一只宠物有关的人：

select owner
from pets
where (animal, color) in ( ('dog', 'black'), ('cat', 'green'))

这也会归还只有黑狗或绿猫的主人，所以我们需要过滤掉那些有两只动物的人，可以使用group by和having条款来完成

select owner
from pets
where (animal, color) in ( ('dog', 'black'), ('cat', 'green'))
group by owner
having count(*) = 2;

SQLFiddle示例：http://sqlfiddle.com/#!15/4df52/1