How to use aggregate function in update in SQL server 2012 - sql

Question

I Tried as shown below:
CREATE TABLE #TEMP
(
ID INT,
EmpID INT,
AMOUNT INT
)
INSERT INTO #TEMP VALUES(1,1,10)
INSERT INTO #TEMP VALUES(2,1,5)
INSERT INTO #TEMP VALUES(3,2,6)
INSERT INTO #TEMP VALUES(4,3,8)
INSERT INTO #TEMP VALUES(5,3,10)
.
.
.
SELECT * FROM #TEMP
ID EmpID AMOUNT
1 1 10
2 1 5
3 2 6
4 3 8
5 4 10
UPDATE #TEMP
SET AMOUNT = SUM(AMOUNT) - 11
Where EmpID = 1
Expected Output:
Table consists of employeeID's along with amount assigned to Employee I need to subtract amount from amount filed depending on employee usage. Amount "10" should be deducted from ID = 1 and amount "1" should be deducted from ID = 2.
Amount: Credits available for that particular employee depending on date.
So i need to reduce credits from table depending on condition first i need to subtract from old credits. In my condition i need to collect 11 rupees from empID = 1 so first i need to collect 10 rupee from ID=1 and 1 rupee from the next credit i.e ID=2. For this reason in my expected output for ID=1 the value is 0 and final output should be like
ID EmpID AMOUNT
1 1 0
2 1 4
3 2 6
4 3 8
5 4 10
Need help to update records. Check error in my update statement.

Answer 1

Declare #Deduct int = -11,
#CurrentDeduct int = 0 /*this represent the deduct per row */
update #TEMP
set #CurrentDeduct = case when abs(#Deduct) >= AMOUNT then Amount else abs(#Deduct) end
, #Deduct = #Deduct + #CurrentDeduct
,AMOUNT = AMOUNT - #CurrentDeduct
where EmpID= 1

Answer 2

I think you want the following: subtract amounts from 11 while remainder is positive. If this is true, here is a solution with recursive cte:
DECLARE #t TABLE ( id INT, amount INT )
INSERT INTO #t VALUES
( 1, 10 ),
( 2, 5 ),
( 3, 3 ),
( 4, 2 );
WITH cte
AS ( SELECT * , 17 - amount AS remainder
FROM #t
WHERE id = 1
UNION ALL
SELECT t.* , c.remainder - t.amount AS remainder
FROM #t t
CROSS JOIN cte c
WHERE t.id = c.id + 1 AND c.remainder > 0
)
UPDATE t
SET amount = CASE WHEN c.remainder > 0 THEN 0
ELSE -remainder
END
FROM #t t
JOIN cte c ON c.id = t.id
SELECT * FROM #t
Output:
id amount
1 0
2 0
3 1
4 2
Here I use 17 as start remainder.
If you use sql server 2012+ then you can do it like:
WITH cte
AS ( SELECT * ,
17 - SUM(amount) OVER ( ORDER BY id ) AS remainder
FROM #t
)
SELECT id ,
CASE WHEN remainder >= 0 THEN 0
WHEN remainder < 0
AND LAG(remainder) OVER ( ORDER BY id ) >= 0
THEN -remainder
ELSE amount
END
FROM cte

Answer 3

First you should get a cumulative sum on amount:
select
id,
amount,
sum(amount) over (order by id) running_sum
from #TEMP;
From here we should put 0 on rows before running_sum exceeds the value 11. Update the row where the running sum exceeds 11 and do nothing to rows after precedent row.
select
id,
amount
running_sum,
min(case when running_sum > 11 then id end) over () as decide
from (
select
id,
amount,
sum(amount) over (order by id) running_sum
from #TEMP
);
From here we can do the update:
merge into #TEMP t
using (
select
id,
amount
running_sum,
min(case when running_sum > 11 then id end) over () as decide
from (
select
id,
amount,
sum(amount) over (order by id) running_sum
from #TEMP
)
)a on a.id=t.id
when matched then update set
t.amount = case when a.id = a.decide then a.running_sum - 11
when a.id < a.decide then 0
else a.amount
end;
See an SQLDFIDDLE