Comparing Data in col of 2 tables - with a Calculation

Question

There are 20 records in 2 different tables (A&B). The records pertain to periods between Jan 07 and March 09. There is a business logic that says that all the 15 records which fall between Jan 07 and Dec 08; their amount needs to be changed in Table B. While the amount for remaining 5 records that fall between Jan 09 and March 09 should remain the same. The formulae to be applied for the first 15 records is “amount/.50*0.125” and this result amount should reflect in the new table under the amount column.
Now the task to ensure that the calculation has happened correctly from Table A for those 15 records that fall between Jan 2007 and Dec 2008 in Table B and that the amount is the same for records for period after Jan 2009. I’d only be testing that the new amount after the business logic calculation reflects in the new amount column of Table B.
A sql statement is required for this.
Thanks,
Dush

Answer 1

you might want to give this pseudo code a try
update [2nd table]
   set amount = (select t.amount / .50 * 0.125
                   from (select id, rownum rn, amount
                           from [1st table]
                          where period_date between '01-JAN-07' and '31-MAR-09'
                         order by id) t
                 where  t.rn <= 15
                   and  t.id = [2nd table].id)
where id in (select t.id
                from (select id, rownum rn, amount
                        from [1st table]
                      where period_date between '01-JAN-07' and '31-MAR-09'
                      order by id) t
               where  t.rn <= 15)still it's better if you can post the actual tables, columns, and some sample data