I am trying to add hours quoted per machine. I have to look at three tables to get the correct and most recent data. I was able to get a list of the hours I need to add.

However, I tried all kinds of ways to use a SUM() function but it always gives me aggregate errors.

Here is the SQL Code:

SELECT 
(SELECT TOP 1 change.hours 
    FROM change WHERE change.id = part.id
    ORDER BY change.timeStamp DESC) as 'Hours'

FROM change 
INNER JOIN part ON (part.id = change.id)
INNER JOIN  completed ON (part.id = completed.id) 

WHERE part.id NOT IN (SELECT completed.id FROM completed WHERE completed.completed = 1) 
and (SELECT TOP 1 change.machine FROM change WHERE part.id = change.id ORDER BY change.timeStamp DESC ) = :machine

GROUP BY change.id, part.id

I basically need to single-cell result that will add all the hours per machine. The result will be displayed on GUI.

RESULT SHOULD BE Machine 1 has to be 12 hours Machine 2 has to be 18 hours Machine 3 has to be 18 hours

TABLES

part

change

change

That's great work, Carlos.

I was able to add to your code to get the results I need

There is input of which machine is displaying. :machine is the input.

SELECT ISNULL((
SELECT sum(Hours)
FROM (SELECT 
        (SELECT TOP 1 change.hours 
            FROM change WHERE change.id = part.id
            ORDER BY change.timeStamp DESC) as 'Hours'
    FROM change 
        INNER JOIN part ON (part.id = change.id)
        INNER JOIN  completed ON (part.id = completed.id) 
    
    WHERE part.id NOT IN (SELECT completed.id FROM completed WHERE completed.completed = 1) 
    and (SELECT TOP 1 change.machine FROM change WHERE part.id = change.id ORDER BY change.timeStamp DESC) = :machine
    
    GROUP BY change.id, part.id) as a), 0)