How to find number of subscribers per question?

Question

I am trying to find the number of subscriber per question. The challenge here is that users are subscribing more then once, but I only need to count when that user subscribe the first time. I am still learning please if someone can direct me. I have attached a link the table and code I have used

select * , COUNT(GroupQuestionSubscriberId) NumberOfSubscriber
from [dbo].[ADF_GroupQuestionSubscribers]
where GroupQuestionId = 4654
GROUP BY [GroupQuestionSubscriberId], [GroupQuestionId], [UserID], [Status], [CreatedDt]

Answer 1

The column CreatedDt is very likely to contain unique values for every row of data. Including that column in your group by clause will produce many counts that equal 1 . In order for your current query to produce a count of 2 you need two rows with exactly the same GroupQuestionSubscriberId , GroupQuestionId , UserID , Status and CreatedDt . If all this is not many a lot of sense, then I suggest you brush up on your group by knowledge by reading the documention .

If the intention is to display that count next to the available data , then using a cross apply is a possible solution.

Sample data

create table ADF_GroupQuestionSubscribers
(
  GroupQuestionSubscriberId int,
  GroupQuestionId int,
  UserId int,
  Status nvarchar(10),
  CreatedDt datetime
);

insert into ADF_GroupQuestionSubscribers (GroupQuestionSubscriberId, GroupQuestionId, UserId, Status, CreatedDt) values
(8031, 4654, 32338, 'Subscribed', '2021-01-19 15:41:25.970'),
(8035, 4654, 32299, 'Subscribed', '2021-01-19 15:55:14.123'),
(8038, 4654, 32338, 'Subscribed', '2021-01-19 16:00:27.343'),
(8094, 4654, 32466, 'Subscribed', '2021-01-20 06:42:50.323');

Solution

select gqs.*,
       c.NumberOfSubscribers
from ADF_GroupQuestionSubscribers gqs
cross apply ( select count(distinct gqsc.UserId) as NumberOfSubscribers
              from ADF_GroupQuestionSubscribers gqsc
              where gqsc.GroupQuestionId = gqs.GroupQuestionId ) c
where gqs.GroupQuestionId = 4654;

Result

GroupQuestionSubscriberId  GroupQuestionId  UserId  Status      CreatedDt                NumberOfSubscribers
-------------------------  ---------------  ------  ----------  -----------------------  -------------------
8031                       4654             32338   Subscribed  2021-01-19 15:41:25.970  3
8035                       4654             32299   Subscribed  2021-01-19 15:55:14.123  3
8038                       4654             32338   Subscribed  2021-01-19 16:00:27.343  3
8094                       4654             32466   Subscribed  2021-01-20 06:42:50.323  3

Fiddle to see things in action.

Edit: solution updated with new expected result information.