Where clause on Running total - sql

Question

I have this table which stores containers by region and the number of coffee pouches in each of the containers.
if object_id( 'dbo.Container' ) is not null
drop table dbo.Container
go
create table dbo.Container
(
Id int not null,
Region int not null,
NumberOfCoffeePouches int not null,
constraint pkc_Container__Id primary key clustered(Id asc)
)
go
insert into dbo.Container
( Id , Region , NumberOfCoffeePouches )
values
( 1, 1, 10 ),
( 2, 1, 30 ),
( 3, 1, 5),
( 4, 1, 7),
( 5, 1, 1),
( 6, 1, 3),
( 7, 2, 4),
( 8, 2, 4),
( 9, 2, 4)
I need to list out the container Ids that will be used to fulfill an order of, say 50, coffee pouches. Over supplying is OK.
Here is query I have come up with
declare #RequiredCoffeePouches int = 50
select
sq2.Id,
sq2.NumberOfCoffeePouches,
sq2.RunningTotal,
sq2.LagRunningTotal
from
(
select
sq1.Id,
sq1.NumberOfCoffeePouches,
sq1.RunningTotal,
lag(sq1.RunningTotal, 1, 0) over (order by sq1.Id asc)
as 'LagRunningTotal'
from
(
select
c.Id,
c.NumberOfCoffeePouches,
sum(c.NumberOfCoffeePouches)
over (order by c.Id asc) as 'RunningTotal'
from
dbo.Container as c
where
c.Region = 1
) as sq1
) as sq2
where
sq2.LagRunningTotal <= #RequiredCoffeePouches
It gives the expected result
Id NumberOfCoffeePouches RunningTotal LagRunningTotal
----------- --------------------- ------------ ---------------
1 10 10 0
2 30 40 10
3 5 45 40
4 7 52 45
Question:
Is there a better and more optimized way to achieve this?
Specially the Container table is very large table and I think the sub query sq1 will unnecessarily calculate the RunningTotals for all the containers in the region. I was wondering if there is anyway to have sq1 stop processing more rows once the RunnningTotal exceeds over the #RequiredCoffeePouches.

Answer 1

Two things:
Moving your WHERE clause inside of the relevant sub-select can greatly increase the speed of the query because it'll pull less data. Using your example:
SELECT
sq2.Id,
sq2.NumberOfCoffeePouches,
sq2.RunningTotal,
sq2.LagRunningTotal
FROM
(
SELECT
sq1.Id,
sq1.NumberOfCoffeePouches,
sq1.RunningTotal,
lag(sq1.RunningTotal, 1, 0) over (order by sq1.Id asc) AS 'LagRunningTotal'
FROM
(
SELECT
c.Id,
c.NumberOfCoffeePouches,
SUM(c.NumberOfCoffeePouches) OVER (order by c.Id asc) AS 'RunningTotal'
FROM dbo.Container AS c
WHERE c.Region = 1
) AS sq1
WHERE sq2.LagRunningTotal <= #RequiredCoffeePouches
) AS sq2
CTEs can also improve performance:
;WITH sql1CTE AS (
SELECT
c.Id,
c.NumberOfCoffeePouches,
SUM(c.NumberOfCoffeePouches) OVER (order by c.Id asc) AS 'RunningTotal'
FROM dbo.Container AS c
WHERE c.Region = 1
),
sql2CTE AS (
SELECT
Id,
NumberOfCoffeePouches,
RunningTotal,
lag(RunningTotal, 1, 0) over (order by Id asc) AS 'LagRunningTotal'
FROM sql1CTE
WHERE LagRunningTotal <= #RequiredCoffeePouches
)
SELECT
Id,
NumberOfCoffeePouches,
RunningTotal,
LagRunningTotal
FROM sql2CTE
SQL Server CTE Basics
If you're using SSMS, select "Include Client Statistics" and "Include Actual Execution Plan" to keep track of how your query performs while you're crafting it.