[英]Selecting a COUNT of values, grouped by that same column, distinct on another
這是一個示例架構:
| type_id | university_id |
---------------------------
| 1 | u01 |
| 2 | u01 |
| 2 | u01 |
| 3 | u02 |
| 4 | u02 |
我想要的是對具有相同university_id
, university_id
本身的記錄數量進行計數,並且它一定不能包含type_id
重復項,因此對於上面給出的相同數據,結果看起來像這樣:
| university_id | COUNT(university_id) |
----------------------------------------
| u01 | 2 |
| u02 | 2 |
現在,我正在嘗試以下操作,但是它顯然會給我COUNT(u01)
3
而不是2
SELECT university_id, COUNT(university_id) FROM table GROUP BY university_id
是否可以做我想做的事情,如果可以,怎么做?
您應該按type_id
唯一地計數,而不type_id
university_id
計數
SELECT university_id, COUNT(DISTINCT type_id) TotalCount
FROM tableName
GROUP BY university_id
您需要在type_id
列上添加一個count(distinct)
:
select university_id, count(distinct type_id)
from table
group by university_id
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