Previous and Prior Year Date Values

Question

How do I get the Previous, Prior year month and Prior year previous month values from a given date?
Ex: Input would be: 05/01/2008
The output should be:
05/01/2008 - Current Month
04/01/2008 - Previous Month for the Current Year
05/01/2007 - Prior year current Month
04/01/2007 - Prior Year Previous Month
Please let me know..

Answer 1

Hi,
Then you'll probably do a self-join. In one copy of the table, you'll get the data from date d1, and in the other copy, you'll get the data from date ADD_MONTHS (d1, -12).
If, ultimately, you are going to show four sets of figures (from four different rows representing four different dates) on the same output line, then you may find it more convenient to do a pivot rather than a self-join. Search for the buzz word "pivot" and you'll get lots of examples. You might start by selecting four rows:
WHERE   dt IN
        ( d1
        , ADD_MONTHS (d1, -1)
        , ADD_MONTHS (d1, -12)
        , ADD_MONTHS (d1, -13)
        ) ...and then pivoting that data into four columns:
SELECT  ...
,       MAX (CASE WHEN dt = d1                   THEN val END) AS this_month
,       MAX (CASE WHEN dt = ADD_MONTHS (d1, -1)  THEN val END) AS one_month_ago
,       MAX (CASE WHEN dt = ADD_MONTHS (d1, -12) THEN val END) AS one_year_ago
,       MAX (CASE WHEN dt = ADD_MONTHS (d1, -13) THEN val END) AS thirteen_months_ago
...