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 that original design is a bit off, hence the complexity. The design below suggests daily (or more frequent) entries, but only count for the day, for a specific application, by a specific person. The Kimball star schema allows for easy slicing and dicing by date, by month, by year, by application, by person, by job title etc.

For example, across all applications in years 2008, 2009, 2010

SELECT  sum(TestCount) AS "Test Count"
FROM    factTest AS f
        JOIN dimApplication AS a ON a.ApplicationID = f.ApplicationID
        JOIN dimPerson AS p ON p.PersonID = f.PersonID
        JOIN dimDate AS d ON d.DateID = f.DateID
WHERE [Year] BETWEEN 2008 AND 2010

Across all applications in year 2009, only on Fridays

WHERE [Year] = 2009 AND DayOfWeek = 'Friday'

Across all applications in year 2009, by person.

SELECT  FullName, sum(TestCount) AS "Test Count"
FROM    factTest AS f
        JOIN dimApplication AS a ON a.ApplicationID = f.ApplicationID
        JOIN dimPerson AS p ON p.PersonID = f.PersonID
        JOIN dimDate AS d ON d.DateID = f.DateID
WHERE [Year] = 2009
GROUP BY FullName

By application, by person, by month in year 2009, but only on weekends

SELECT  ApplicationName, FullName, [MonthName], sum(TestCount) AS "Test Count"
FROM    factTest AS f
        JOIN dimApplication AS a ON a.ApplicationID = f.ApplicationID
        JOIN dimPerson AS p ON p.PersonID = f.PersonID
        JOIN dimDate AS d ON d.DateID = f.DateID
WHERE [Year] = 2009 AND IsWeekend = 'Yes'
GROUP BY ApplicationName, FullName, [MonthName]

Across all applications for years 2000-2009, by year, by month, but only for tests done by a receptionist on Tuesdays.

SELECT  [Year], [Month], sum(TestCount) AS "Test Count"
FROM    factTest AS f
        JOIN dimApplication AS a ON a.ApplicationID = f.ApplicationID
        JOIN dimPerson AS p ON p.PersonID = f.PersonID
        JOIN dimDate AS d ON d.DateID = f.DateID
WHERE   [Year] BETWEEN 2000 AND 2009
        AND JobTitle = 'Receptionist'
        AND DayOfWeek = 'Tuesday'
GROUP BY [Year], [Month]

Across all applications, for year 2009, tests done on weekends by short people who own two or more cats.

SELECT  sum(TestCount) AS "Test Count"
FROM    factTest AS f
        JOIN dimApplication AS a ON a.ApplicationID = f.ApplicationID
        JOIN dimPerson AS p ON p.PersonID = f.PersonID
        JOIN dimDate AS d ON d.DateID = f.DateID
WHERE [Year] = 2009
      AND IsWeekend = 'Yes'
      AND IsShortPerson ='Yes'
      AND CatsOwned >= 2

Etc...

The syntax is sql server, but there is nothing special here.

UPDATE
Notice that FROM ... JOIN ... JOIN ... JOIN ... is always the same. All slicing and dicing is done via SELECT, WHERE, and GROUP BY -- no "complex queries" required.