SQL要爲我的訂戶選擇唯一域計數？

Question

我試圖找出我從每個域都有用戶數量，雅虎，谷歌，AOL的....

這裏是我想出了但不分組，因爲我認爲這將

select SUBSTRING(EmailAddress, PATINDEX('%@%', EmailAddress) +1, LEN(EmailAddress) -PATINDEX('%@%', EmailAddress)) As [Domain], COUNT(SUBSTRING(EmailAddress, PATINDEX('%@%', EmailAddress) +1, LEN(EmailAddress) - PATINDEX('%@%', EmailAddress))) As [Count] 
from Subscribers 
GROUP BY EmailAddress 

結果是這樣的

yahoo.com 1 
gmail.com 1 
yahoo.com 1 

我想要的東西更多類似這樣的

yahoo.com 2 
gmail.com 1 

Answer 1

問題是，您正在按emailaddress分組，這不是domain的值。如果電子郵件地址包含john@yahoo.com或jim@yahoo.com，因爲這些地址是唯一的，所以當您將組計數分隔時。

如果你想組由域值，那麼你需要GROUP BY你計算formala域：

select SUBSTRING(EmailAddress, PATINDEX('%@%', EmailAddress) +1, LEN(EmailAddress) -PATINDEX('%@%', EmailAddress)) As [Domain], 
    COUNT(SUBSTRING(EmailAddress, PATINDEX('%@%', EmailAddress) +1, LEN(EmailAddress) - PATINDEX('%@%', EmailAddress))) As [Count] 
from Subscribers 
GROUP BY SUBSTRING(EmailAddress, PATINDEX('%@%', EmailAddress) +1, LEN(EmailAddress) -PATINDEX('%@%', EmailAddress)); 

或者你可以通過domain別名使用子查詢，然後組：

select domain, 
    count(*) [count] 
from 
(
    select SUBSTRING(EmailAddress, PATINDEX('%@%', EmailAddress) +1, LEN(EmailAddress) -PATINDEX('%@%', EmailAddress)) As [Domain] 
    from Subscribers 
) d 
group by domain;