MySQL的數量和組由兩個不同的列

Question

我有一個表recommendation與領域recommender，attractionid

我要算如何表羣組中存在由attractionid許多attractionid但如果有相同的對recommender和attractionid它們被算作1 例如，

attractionid recommender 
     1    1 
     1    2 
     1    1 
     2    3 
     2    1 
     2    2 
     2    2 
     2    2 

預期的結果：

attractionid count 
     1   2 
     2   3 

個

行下面應該算作1

attractionid recommender 
      1    1 
      1    1 
      2    2 
      2    2 
      2    2 

Answer 1

使用distinct attractionid,recommender內部count功能。

查詢

select attractionid, 
count(distinct attractionid,recommender) as `count` 
from recommendation 
group by attractionid; 

Answer 2

嘗試：

select attractionid, count(recommender) cnt 
from (
    select distinct attractionid, recommender 
    from recommendation 
) x 
group by attractionid