update a field based on subtotal from another table

Question

Hi all,

I'm using oracle(10).

I've got two tables as follows:

Table1 (uniq rows):
ID    AMOUNT     DATE 

Table2:
ID    AMOUNT1 AMOUNT2 ...AMOUNTN DATE

Table2 is connected many to one to Table1 connected via ID.

What I need is update-ing Table1.DATE with: the last (earliest) date from Table2 where Table1.AMOUNT - SUM(Table2.AMOUNT1) <= 0, when reading table 2 backwards by the Table2.DATE field.

Is there a simple way to do it?

Thanks in advance!

UPDATE: as I see from your answers I had misspecified the question a bit. So here goes a detailed example:

Table1 has:

ID: 1     AMOUNT:100    DATE:NULL

Table2 has (for ID: 1 so ID is not listed in here):

AMOUNT1     DATE
50          20080131
30          20080121
25          20080111
20          20080101

So in this case I need 20080111 as the DATE in Table1 as 50+30+25 => 100.

Answer 1

Based on your revised question, this is a case for using analytic functions.

Assuming you meant >=100 rather than <= 100 as your example implies, and renaming columns DATE to THEDATE since DATE is a reserved word in Oracle:

update table1 set thedate=
( select max(thedate) from
  ( select id, thedate,
           sum(amount1) over (partition by id  order by thedate desc) cumsum
    from table2
  ) v
  where v.cumsum >= 100
  and v.id = table1.id
)

If the 100 means the current value of table1 then change that line to:

  where v.cumsum >= table1.amount

Answer 2

First off - your database layout feels severely wrong, but I guess you can't / don't want to change it. Table1 should probably be a view, and Table2 does not make the impression of proper normalization. Something like (ID, AMOUNT_TYPE, AMOUNT_VALUE, DATE) would make much more sense to me.

But to solve your problem (this is T-SQL "UPDATE FROM" syntax, but I think Oracle knows it):

UPDATE 
  Table1
SET
  Date = Table2Aggregate.MinDate
FROM
  Table1 
  INNER JOIN (
    SELECT Id, SUM(Amount1) SumAmount1, MIN(Date) MinDate 
    FROM Table2 
    GROUP BY Id
  ) AS Table2Aggregate ON Table1.Id = Table2Aggregate.ID 
WHERE
  Table1.Amount - Table2Aggregate.SumAmount1 <= 0