Question

I have 2 tables UserSession and Sale.

Table User has 4 columns, namely UserID, UserSessionID, SessionOpenDate and SessionCloseDate.

Table Sale has 2 columns, which are price, cost, userID and CompletedDate.

When a user logs in, a new row is created in the User table, where the user’s login timestamp will be saved in the SessionOpenDate and a new UserSessionID will be assigned to the session. When the user logs off, the log off timestamp will be be saved in SessionCloseDate.

When the user is still logged in, the user can make some sale and the sale information is saved in the Sale table. The timestamp when the sale is finalized in saved in CompletedDate column.

For some reason, I need to get the all sales done in a certain UserSessionID where the CompletedDate must be within the SessionOpenDate and SessionCloseDate. However, if the user has not logged off yet, which means that the value in SessionCloseDate is null, the CompletedDate should be between SessionOpenDate and now.

Here’s my query:

SELECT SUM(s.cost) AS Cost, SUM(s.price) AS Price
FROM Sale AS s 
  INNER JOIN UserSession AS u 
  ON s.userID = u.userID
WHERE 
  (s.CompletedDate >=
    ( SELECT SessionOpenDate
      FROM UserSession
      WHERE (UserSessionID = u.UserSessionID)
)
  ) 
  AND 
  (s.CompletedDate < 
    ( 
      IF EXISTS
       (    
         SELECT SessionCloseDate AS closeTime
         FROM UserSession AS UserSessionTemp
         WHERE (UserSessionID = u.UserSessionID)
       ) 
       BEGIN
         SET closeTime = SELECT CURRENT_TIMESTAMP
       END
    )
  ) 
  AND u.UserSessionID IN (1) 

However, Sql Server says Incorrect syntax near the keyword 'IF'. and Incorrect syntax near ')'.

Can anyone tell me what went wrong with my IF block?

Answer 1

You can’t use an IF block inside a SELECT statement. Also, I don’t know what you’re really trying to accomplish with SET, since closeTime is not a variable/parameter.

You can use IIF in SQL Server 2012 (syntactical sugar for CASE WHEN <condition> THEN <true_value> ELSE <false_value> END – use this syntax for earlier versions):

IIF(EXISTS
   (    
     SELECT SessionCloseDate AS closeTime
     FROM UserSession AS UserSessionTemp
     WHERE (UserSessionID = u.UserSessionID)
   ), (
     SELECT SessionCloseDate AS closeTime
     FROM UserSession AS UserSessionTemp
     WHERE (UserSessionID = u.UserSessionID)
   ),  
     CURRENT_TIMESTAMP
)

---

Honestly, without getting too complicated, here’s what I would do instead:

SELECT SUM(s.cost) AS Cost, SUM(s.price) AS Price
FROM userSession AS u
INNER JOIN Sale AS s ON u.userID = s.userID 
WHERE u.UserSessionID = @UserSessionId
AND s.CompletedDate >= u.SessionOpenDate 
AND (u.SessionCloseDate IS NULL OR s.CompletedDate < u.SessionCloseDate)

Or,

SELECT SUM(s.cost) AS Cost, SUM(s.price) AS Price
FROM userSession AS u
INNER JOIN Sale AS s ON u.userID = s.userID 
WHERE u.UserSessionID = @UserSessionId
AND s.CompletedDate BETWEEN u.SessionOpenDate 
                    AND COALESCE(u.SessionCloseDate, '12/31/9999 23:59:59.9999')