选择值的计数，由同一列编组，不同的另一

Question

下面是一个示例模式：

| type_id | university_id | 
--------------------------- 
| 1 |  u01  | 
| 2 |  u01  | 
| 2 |  u01  | 
| 3 |  u02  | 
| 4 |  u02  | 

而且我想是的具有相同university_id记录数的计数中，university_id本身，它不能包括type_id重复的，所以结果看起来像这样由于上述相同的数据：

| university_id | COUNT(university_id) | 
---------------------------------------- 
|  u01  |   2   | 
|  u02  |   2   | 

现在，我尝试以下，但它显然给我一个COUNT(u01)Ø ˚F3代替2

SELECT university_id, COUNT(university_id) FROM table GROUP BY university_id 

是否可以做我想做的，如果又如何？

Answer 1

你应该type_id算唯一没有被university_id

SELECT university_id, COUNT(DISTINCT type_id) TotalCount 
FROM tableName 
GROUP BY university_id 

• SQLFiddle Demo

Answer 2

您在type_id列需要count(distinct)：

select university_id, count(distinct type_id) 
from table 
group by university_id