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

"Select count of unit tests across all applications where the application data_added is the latest date added for that application id"

I'm afraid all I can say it that this formulation-of-requirement seems necessarily flawed.

First, the only "free variable" in your query (i.e. the only parameter) seems to be "that application ID".

So your problem statement seems to be :

(1) Given an application ID, get me the latest (i.e. MAX(...)) date_added of that application ID. (2) Given that latest date, give me all the applications that have a date_added that is equal to the result of (1) (3) Given that set of applications, give me the count of unit tests "across those applications"

Second : with respect to "across those applications", I must say that neither my understanding of relational algebra nor my understanding of natural language helps me the remotest bit to understand what it is (PRECISELY) that you mean.