如何找到行，其中同一列只有同另一列

Question

假设如下表：

Name Age Occupation 
Alex 20 Student 
Alex 20 Seller 
Alex 20 Minister 
Liza 19 Student 
Liza 20 Volunteer 
Liza 21 HR partner 

我想找到具有唯一（只）20年龄列名。所以从这张桌子我想要所有“亚历克斯”行，并没有“丽莎”行。 谢谢！

Answer 1

您需要使用Group By和Having子句。试试这个方法只

select Name 
from table 
group by Name 
having count(case when Age = 20 then 1 end) = count(*) 

count(case when Age = 20 then 1 end)计数时age = 20如果它等于总数则名只有20年龄。使用NOT IN()

Answer 2

方式一：

SELECT Name, Age, Occupation 
FROM YourTable 
WHERE Age = 20 
AND Name NOT IN (SELECT Name FROM YourTable WHERE Age <> 20) 

Answer 3

只要一另一种方式：

select Name 
from table 
group by Name 
having min(Age) = 20 and max(Age) = 20