Question

我有这张桌子，我需要知道艺术家在他/她的职业生涯中有多少张专辑，为了简洁起见，我只发布一位艺术家。

"artist_ID" "song_ID" "album_ID" "touring"
"57"      "98"       "48"      "No"        
"57"      "99"       "48"      "No"        
"57"      "100"      "48"      "Sí"        
"57"      "101"      "48"      "No"        
"57"      "102"      "48"      "No"        
"57"      "103"      "48"      "No"        
"57"      "104"      "48"      "No"        
"57"      "105"      "48"      "No"        
"57"      "106"      "48"      "No"        
"57"      "279"      "163"     "No"        
"57"      "280"      "163"     "No"        
"57"      "281"      "163"     "No"        
"57"      "380"      "241"     "No"        
"57"      "381"      "241"     "No"

然后通过这个获取数据：

SELECT artist_ID,
    count(*) AS churned_albums
FROM relation
GROUP BY group_ID,
    album_ID;

我希望得到以下数据：

"artist_ID" "churned_albums"           
"57"      "3"

但是，唉，我明白了：

"artist_ID" "churned_albums"
"57"      "9"             
"57"      "3"             
"57"      "2"

它正在计算每张专辑的每首歌曲，我不知道如何告诉MySQL忽略这些歌曲，只计算专辑。我还尝试count(artist_ID)而不是count(*)以及其他几种排列，但似乎没有任何效果。

此问题与How to use count and group by at the same select statement和Using group by on multiple columns密切相关，但它们没有帮助。：（

感谢您的帮助！：）

Answer 1

我创建了一个 sqlfiddle ，用于显示所需的查询。看看这里：http://sqlfiddle.com/#!9/d1372/2

我使用的查询：

select group_id, count(distinct album_id) AS churned_albums
from relations
group by group_id;

Answer 2

您可以使用count(distinct album_id)计算每group_id

个唯一相册的数量

select group_id,
    count(distinct album_id) as churned_albums
from relation
group by group_id

分组并计算不返回我的期望

2 个答案: