SQL query aggregate data for week - db2 ver7

I wanted to run a query to calculate peak per week from a table that has date time value column and the table has data for a day, I wanted to aggregate on that data for a week and find the peak value.

date time field is looking like this For Apr1 data  2006-04-01-00.00.00 starting to 2006-04-30-23:59:00 to end.

I wanted to aggregate the value for a week like starting Apr1-7,8-14,15-22,23-30 on a number column (amount) and then find the peak value (I suppose we can use max ) and get the value in 1 SQL query.

Any ideas
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if you table is something like this:

create table agg(
   dt date,
   amount integer

you can use this:

          when day(dt) >= 1 and day(dt) <= 7 then 'APR_1-7'
          when day(dt) >= 8 and day(dt) <= 14 then 'APR_8-14'
          when day(dt) >= 15 and day(dt) <= 21 then 'APR_15-21'
          when day(dt) >= 22 and day(dt) <= 28 then 'APR_22-28'
          when day(dt) >= 29 and day(dt) <=30 then 'APR_29-30'
      end as weekEnding,
      max(amount) as amount
from agg
group by
      when day(dt) >= 1 and day(dt) <= 7 then 'APR_1-7'
      when day(dt) >= 8 and day(dt) <= 14 then 'APR_8-14'
      when day(dt) >= 15 and day(dt) <= 21 then 'APR_15-21'
      when day(dt) >= 22 and day(dt) <= 28 then 'APR_22-28'
      when day(dt) >= 29 and day(dt) <=30 then 'APR_29-30'

i would assume that maybe you'd use a procedure to make this more universal for different months...

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This should be general:

SELECT monday, weekamount
  FROM (SELECT SUM(amount) AS weekamount, monday
               FROM (SELECT dt - dayofweek_iso(dt) days + 1 day AS monday,
                            FROM agg) AS X
             GROUP BY monday) AS Y

The usage of ORDER BY and FFRO allows you to retrieve the beginning date of the week without having to do a rejoin.
I chose to normalize to a specific date instead of grouping by year and week directly because the last week of the year would be hard to group properly.

Of course the inner subquery is not strictly needed. I simply didn't want to repeat the expression in the group by clause.

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