Calculate percent increase/decrease from previous row value

Question

I have a table that looks something like this:

|date_start  | date_end    |amount | 
+------------+-------------+-------+
|2015-02-23  | 2015-03-01  |50              


        

Answer 1

If we assume that the previous row always ends exactly one day before the current begins (as in your sample data), then you can use a join. The percentage increase would be:

select t.*,
       100 * (t.amount - tprev.amount) / tprev.amount
from atable t left join
     atable tprev
     on tprev.date_end = t.date_start - interval 1 day;

However, your results seem to just have the difference, which is easier to calculate:

select t.*,
       (t.amount - tprev.amount) as diff
from atable t left join
     atable tprev
     on tprev.date_end = t.date_start - interval 1 day;