'strftime' is not a recognized built-in function name

Question

I am using Microsoft SQL Database Management Studio and it will not allow me to use the strftime() function to run a query. I have to create a table by months with new users and

Answer 1

strftime is a mysql function, and isn't available in Microsoft's sql-server.

For this simple usecase (extracting a month from a date), you could user month:

SELECT   MONTH(createddate) AS [Month], 
         COUNT(createddate) AS [Subscribers],
         COUNT(dateunsubscribed) AS [UNsubscribers]
FROM     subscriber
GROUP BY 1
ORDER BY 1;

EDIT:
To address the question in the comment, the group by clause doesn't take an ordinal like the order by clause does. You'll need to specify the expression you want to group by:

SELECT   MONTH(createddate) AS [Month], 
         COUNT(createddate) AS [Subscribers],
         COUNT(dateunsubscribed) AS [UNsubscribers]
FROM     subscriber
GROUP BY 1
ORDER BY MONTH(createddate);