How to calculate the slope in SQL

Question

I have some data in a sql database and I\'d like to calculate the slope. The data has this layout:

Date        |  Keyword  |  Score    
2012-01-10  |  ipad          


        

Answer 1

If you're defining slope as just the slope from the earliest point to the latest point, and if score only increases with date, then you can get the output above with this:

SELECT *
  FROM scores
  JOIN
    (SELECT foo.keyword,
            (MAX(score)-MIN(score)) / DATEDIFF(MAX(date),MIN(date)) AS score
     FROM scores
     GROUP BY keyword) a
  USING(keyword);

However if you want linear regression, or if scores can decrease as well as increase with time, you'll need something more complex.