Question

Below is a sample query of what I am trying to do and it gets the job done but I feel like the sub queries are not the best way to go here. Any pointers?

SELECT DISTINCT
    u.UserID,   
    (SELECT COUNT(LoginID) FROM Logins WHERE Success = 1 AND UserID = u.UserID) AS Successful,
    (SELECT COUNT(LoginID) FROM Logins WHERE Success = 0 AND UserID = u.UserID) AS Unsuccessful,        
    (SELECT TOP 1 LoginDate FROM Logins WHERE UserID = u.UserID ORDER BY LoginDate DESC) AS LastLogin
FROM 
    Users u INNER JOIN 
    Logins l ON u.UserID = l.UserID

BTW the above example doesn’t look like it needs the join but in the real solution I do to get some other columns…

Answer 1

Am I missing something significant, or could you not do this with a single aggregate query?

SELECT u.UserID,
    SUM(CASE WHEN Success = 1 THEN 1 ELSE 0 END) AS Successful,
    SUM(CASE WHEN Success = 0 THEN 1 ELSE 0 END) AS Unsuccessful,
    MAX(LoginDate) AS LastLogin
FROM Users u
INNER JOIN Logins l on u.UserID = l.UserID
GROUP BY u.UserID