Question

I have an Access .mdb database with a Table that looks similar to:

+---------+------+--------+
|     date        | value |
+---------+------+--------+
|2011-05-04 12:00 | 45.9  |
|2011-05-05 12:00 | 21.2  |
|2011-05-06 12:00 | 32.2  |
|2011-05-07 12:00 | 30.4  |
|2011-05-08 12:00 | 40.4  |
|2011-05-09 12:00 | 19.8  |
|2011-05-10 12:00 | 29.7  |
+-------+---------+-------+

I would like to create a query that will return values that are derived from subtracting one value from a previous day value.

For example: The query would calculate
(21.2-45.9) and return -24.7
(32.2-21.2) and return -11.0
(30.4-32.2) and return -1.8
etc

How can I accomplish this in a SELECT statement?

Answer 1

Here’s the query that worked for me:

SELECT t2.date, t2.value-t1.value
FROM Table1 AS t1, Table1 AS t2
WHERE t2.date=DATEADD("d",1,t1.date);

Thanks again, Tom H.