How to update table based on the values in other columns

Question

Here is a sample below, I want to update AvailableAmt column based on the amount entered on UI.

Requirement

Update the value from the last row to the first row,

1. If entered 500 on UI, then the table will be like

2. If entered 1000 on UI, then the table will be like

Thank you for your help in advance !

Answer 1

Can't test it on a Sybase somewhere.
But in theory something like this might work:

DECLARE @Group VARCHAR(8) = 'a';
DECLARE @Amount INT = 1100;

UPDATE t
SET t.AvailableAmt = 
  CASE 
  WHEN q.PrevRemain > 0 AND t.AvailableAmt <= q.PrevRemain THEN 0
  WHEN q.PrevRemain > 0 THEN t.AvailableAmt - q.PrevRemain
  ELSE t.AvailableAmt
  END
FROM YourTable t
JOIN
(
    select [Group], [Row], 
     @Amount-(SUM(AvailableAmt) OVER (PARTITION BY [Group] ORDER BY AvailableAmt, [Row] desc) - AvailableAmt) as PrevRemain
    from YourTable
    where AvailableAmt > 0
      and [Group] = @Group
) AS q
ON (q.[Group] = t.[Group] and q.[Row] = t.[Row]);

For a Sybase flavor that doesn't support the window function of SUM, something like this might work.

DECLARE @Group VARCHAR(8) = 'a';
DECLARE @Amount INT = 1200;

UPDATE t
SET t.AvailableAmt = 
  CASE 
  WHEN q.PrevRemain > 0 AND t.AvailableAmt <= q.PrevRemain THEN 0
  WHEN q.PrevRemain > 0 THEN t.AvailableAmt - q.PrevRemain
  ELSE t.AvailableAmt
  END
FROM YourTable t
JOIN
(
    select t1.[Group], t1.[Row], 
     @Amount - (SUM(t2.AvailableAmt)-t1.AvailableAmt) as PrevRemain
    from YourTable t1
    left join YourTable t2 on (t2.[Group] = t1.[Group]  and t2.AvailableAmt <= t1.AvailableAmt and t2.[Row] >= t1.[Row])
    where t1.AvailableAmt > 0
      and t1.[Group] = @Group
    group by t1.[Group], t1.[Row], t1.AvailableAmt
) AS q 
ON (q.[Group] = t.[Group] and q.[Row] = t.[Row]);