Database design - how do I track information over time and query a table for latest data?

Question

We are trying to track our applications in our department and our unit test usage so I have created a database to keep track of this. I have an Applications

Answer 1

I think people seem to be making this harder than it is.

To resolve this you need two queries:

1. Find me the latest entry for each application ID
2. Using the latest entry for each application ID give me the sum of the unit test counts.

SQL for the first is:

SELECT application_ID, MAX(date_added) AS lastDateAdded FROM UnitTestTracking GROUP BY application_ID

For the second we make this work by nesting queries:

SELECT 
    SUM(unittestcount) 
FROM 
    UnitTestTracking JOIN 
    (SELECT 
         application_ID, MAX(date_added) AS lastDateAdded 
     FROM 
         UnitTestTracking GROUP BY application_ID) T 
    ON UnitTestTracking.application_ID = T.application_ID AND 
       UnitTestTracking.date_added = T.LastDateAdded

And that should give you what you need i.e. the current total number of unit tests.