Column Sum in Select Query - sql

Question

I have problem in sql server select query. I have following table.
ID-----Name----Quantity
1-------a-----------10
2-------b-----------30
3-------c-----------20
4-------d-----------15
5-------e-----------10
6-------f-----------30
7-------g-----------40
I want to select those record where the sum of Quantity < value. For example if I say select those record where the Quantity sum <65 then the output will be
ID-----Name----Quantity
1-------a-----------10
2-------b-----------30
3-------c-----------20
because if we include the next record then the sum of Quantity will 75.
I want to create this query. Please help me out.

Answer 1

You can simply use a correlated subquery to do so, and it will work fine for both MySQL, and SQL Server. But it is not the best performance wise solution:
SELECT
ID,
Name,
Quantity
FROM
(
SELECT
t1.ID,
t1.Name,
t1.Quantity,
(SELECT SUM(t2.Quantity)
FROM tablename AS t2
WHERE t2.ID <= t1.ID) AS Total
FROM Tablename AS t1
) AS t
WHERE Total < 65;
See it in action:
SQL Fiddle Demo
This will give you:
| ID | NAME | QUANTITY |
------------------------
| 1 | a | 10 |
| 2 | b | 30 |
| 3 | c | 20 |

Answer 2

Best performance wise solution is using recursive CTE.
WITH CTE_Prepare AS
(
SELECT
*,
ROW_NUMBER() OVER (ORDER BY id) AS RN
FROM TableRT
)
, CTE_Recursive AS
(
SELECT ID, Name, Quantity, QUantity AS SumQuantity, RN FROM CTE_Prepare WHERE RN = 1
UNION ALL
SELECT p.ID, p.Name, p.Quantity, r.SumQuantity + p.Quantity AS SumQuantity, r.RN + 1 AS RN FROM CTE_Recursive r
INNER JOIN CTE_Prepare p ON p.RN = r.RN+1
WHERE r.SumQuantity + p.Quantity < 65
)
SELECT *
FROM CTE_Recursive
OPTION (MAXRECURSION 0)
The first CTE is just to calculate ROW_NUMBERS to use instead of your IDs, because it's important not to have gaps and we can't usually be sure with any ID that it would be the case.
Second CTE is two-part recursive, adding Quantity for each next row. You can google about SQL Server recursive CTEs more if needed.
I think this is better then any other approach to find running totals (that's what this concept is called) because it only works with two rows at the time - not adding all previous rows for each calculation and it actually stops as soon it reaches the wanted mark.
SQLFiddle - few rows sample
SQLFiddle - 10000 rows
EDIT: Corrected a few mistakes. In order for this to be fast, WHERE clause needs to be inside CTE and not outside.