SQL when sum of supplies count reach to the demands count? - sql

Question

I want to generate a query in SqlServer 2014 from two tables, have no relation with each other.
The first one represents the demands. And the second one represents the supplies for them.
Demands(
[DemandId] [int] NOT NULL,
[ItemCode] [nvarchar](50) NULL,
[TotalCount] [int] NULL,
[Date] [datetime] NULL)
Supplies(
[SupplyId] [int] NOT NULL,
[ItemCode] [nvarchar](50) NULL,
[Count] [int] NULL,
[Date] [datetime] NULL)
For example, we have a demand with (TotalCount = 1000, ItemCode = 1, Date = d1)
and two Supplies in (Date = d2, Count = 300, ItemCode = 1) and (Date = d3, Count = 700, ItemCode = 1)
the demand finished in d3 Date, so I want a query to indicate when supplies have finished the demands.
consider the following data:
the result should be:
Item01 2020-01-07
Item02 2020-01-06
I appreciate any help.

Answer 1

A simple summary could be...
treat a demand as a negative amount of supply
combine the two datasets in to a single time series
use a cumulative sum to see the net availability
Such as...
WITH
NetContribution AS
(
SELECT [ItemCode], [Date], [Count] FROM Supplies
UNION ALL
SELECT [ItemCode], [Date], -[TotalCount] FROM Demands
)
SELECT
[ItemCode],
[Date],
[Count] AS NetAvailabilityChange,
SUM([Count])
OVER (PARTITION BY [ItemCode]
ORDER BY [Date],
[Count] DESC
)
AS NetAvailability
FROM
NetContribution
While the NetAvailability is negative, Supply has not yet met Demand. While it's positive, Supply has exceeded Demand.
EDIT: In response to your question edit...
Just use the above query and add a WHERE clause...
WITH
NetContribution AS
(
SELECT [ItemCode], [Date], [Count] FROM Supplies
UNION ALL
SELECT [ItemCode], [Date], -[TotalCount] FROM Demands
),
NetAvailability AS
(
SELECT
[ItemCode],
[Date],
[Count] AS Delta,
SUM([Count])
OVER (PARTITION BY [ItemCode]
ORDER BY [Date],
[Count] DESC
)
AS Amount
FROM
NetContribution
)
SELECT
*
FROM
NetAvailability
WHERE
Amount >= 0

Answer 2

This is my source data
Demand :
'1', 'A', '1000', '2020-12-01'
'4', 'B', '2000', '2020-12-01'
Supply :
'2', 'A', '700', '2020-12-05'
'3', 'A', '300', '2020-12-08'
'5', 'B', '1000', '2020-12-05'
'6', 'B', '1000','2020-12-08'
Performed the below query :
select a.itemcode, case when totaldemand - totalsupply = 0 then endsupplydate
else null end enddate from </b>
(
select 'demand' type,itemcode,sum(quantity) totaldemand,min(demanddate) as
date from demand b group by type,itemcode ) b
inner join (
select 'supply' type,itemcode,sum(quantity) totalsupply,max(supplydate) as
endsupplydate from supply group by type,itemcode) a
on a.itemcode = b.itemcode;
Output you will be getting :
ItemCode,DemandStart,SupplyEnd,QuantityLeft
'A', '2020-12-08'
'B', '2020-12-08'

Answer 3

In the absence of using SUM() OVER() to generate a cumulative sum, you can use a triangular join (Join the current row on to all preceding rows), but on large data sets is nastily slow...
WITH
NetContribution AS
(
SELECT [ItemCode], [Date], SUM([Count]) AS [Count]
FROM (
SELECT [ItemCode], [Date], [Count] FROM Supplies
UNION ALL
SELECT [ItemCode], [Date], -[TotalCount] FROM Demands
)
combined
GROUP BY [ItemCode], [Date]
),
NetAvailability AS
(
SELECT
a.[ItemCode],
a.[Date],
a.[Count] AS Delta,
SUM(b.[Count]) AS Amount
FROM
NetContribution AS a
INNER JOIN
NetContribution AS b
ON a.[ItemCode] = b.[ItemCode]
AND a.[Date] >= b.[Date]
GROUP BY
a.[ItemCode],
a.[Date],
a.[Count]
)
SELECT
*
FROM
NetAvailability
WHERE
Amount >= 0
https://dbfiddle.uk/?rdbms=sqlserver_2014&fiddle=48660224fc63bcb2803f5a08b8b1311e