sql query to find the difference in values from previous month - sql-server

Question

I have my sql tables and query as shown below :
CREATE TABLE #ABC([Year] INT, [Month] INT, Stores INT);
CREATE TABLE #DEF([Year] INT, [Month] INT, SalesStores INT);
CREATE TABLE #GHI([Year] INT, [Month] INT, Products INT);
INSERT #ABC VALUES (2013,1,1);
INSERT #ABC VALUES (2013,1,2);
INSERT #ABC VALUES (2013,2,3);
INSERT #DEF VALUES (2013,1,4);
INSERT #DEF VALUES (2013,1,5);
INSERT #DEF VALUES (2013,2,6);
INSERT #GHI VALUES (2013,1,7);
INSERT #GHI VALUES (2013,1,8);
INSERT #GHI VALUES (2013,2,9);
INSERT #GHI VALUES (2013,3,10);
My current query is
I have #Year and #Month as parameters , both integers , example #Year = '2013' , #Month = '11'
SELECT T.[Year],
T.[Month]
-- select the sum for each year/month combination using a correlated subquery (each result from the main query causes another data retrieval operation to be run)
,
(SELECT SUM(Stores)
FROM #ABC
WHERE [Year] = T.[Year]
AND [Month] = T.[Month]) AS [Sum_Stores],
(SELECT SUM(SalesStores)
FROM #DEF
WHERE [Year] = T.[Year]
AND [Month] = T.[Month]) AS [Sum_SalesStores],
(SELECT SUM(Products)
FROM #GHI
WHERE [Year] = T.[Year]
AND [Month] = T.[Month]) AS [Sum_Products]
FROM (
-- this selects a list of all possible dates.
SELECT [Year],
[Month]
FROM #ABC where [Year] = #Year and [Month] = #Month
UNION
SELECT [Year],
[Month]
FROM #DEF where [Year] = #Year and [Month] = #Month
UNION
SELECT [Year],
[Month]
FROM #GHI where [Year] = #Year and [Month] = #Month) AS T;
Which returns
+------+-------+------------+-----------------+--------------+
| Year | Month | Sum_Stores | Sum_SalesStores | Sum_Products |
+------+-------+------------+-----------------+--------------+
| 2013 | | | | |
| 2013 | | | | |
| 2013 | | | | |
+------+-------+------------+-----------------+--------------+
What I want to do is to add more columns to the query which show the difference from the last month. as shown below.
Example : The Diff beside the Sum_Stores shows the difference in the Sum_Stores from last month to this month.
Something like this :
+------+-------+------------+-----------------+-----|-----|---+-----------------
| Year | Month | Sum_Stores |Diff | Sum_SalesStores |Diff | Sum_Products |Diff|
+------+-------+------------+-----|------------+----|---- |----+--------------|
| 2013 | | | | | | | |
| 2013 | | | | | | | |
| 2013 | | | | | | | |
+------+-------+------------+-----|------------+--- |-----|----+---------| ----
Can anyone tell me how I can modify this to achive my goal.

Answer 1

You ca use a CTE and then self join to get the desired result.
Fiddle Here
;WITH DATA AS (
SELECT T.[Year],
T.[Month]
-- select the sum for each year/month combination using a correlated subquery (each result from the main query causes another data retrieval operation to be run)
,
(SELECT SUM(Stores)
FROM #ABC
WHERE [Year] = T.[Year]
AND [Month] = T.[Month]) AS [Sum_Stores],
(SELECT SUM(SalesStores)
FROM #DEF
WHERE [Year] = T.[Year]
AND [Month] = T.[Month]) AS [Sum_SalesStores],
(SELECT SUM(Products)
FROM #GHI
WHERE [Year] = T.[Year]
AND [Month] = T.[Month]) AS [Sum_Products]
FROM (
-- this selects a list of all possible dates.
SELECT [Year],
[Month]
FROM #ABC where [Year] = #Year and [Month] = #Month
UNION
SELECT [Year],
[Month]
FROM #DEF where [Year] = #Year and [Month] = #Month
UNION
SELECT [Year],
[Month]
FROM #GHI where [Year] = #Year and [Month] = #Month
) AS T )
SELECT d1.year,d1.month ,
d1.Sum_Stores , ( isnull(d2.Sum_Stores,0) -d1.Sum_Stores ) AS storeDiff ,
d1.Sum_SalesStores ,( isnull(d2.Sum_SalesStores,0) -d1.Sum_SalesStores ) AS salesStoresDiff,
d1.Sum_Products , ( isnull(d2.Sum_Products,0) -d1.Sum_Products ) AS prodDiff
-- self joining on month -1 to get previous month data
FROM DATA AS d1 LEFT OUTER JOIN DATA AS d2 ON d2.month = d1.month -1
The above query is for illustrative purposes only.The query provided works correctly for the sample data as it contains the data for a year only. You should apply appropriate logic in the on clause of the left outer join to retrieve data which has input data of more than one year.

Answer 2

Try This:
I created a temp table #XYZ with your data and used that to subtract the previous months data. I have to create 2 more variable to take care of spanning years.
If you have any questions, let me know
DECLARE #Year varchar(4)
SET #Year = '2013'
DECLARE #Month varchar(2) set #Month = '1'
DECLARE #DiffYear varchar(4)
Set #DiffYear = DATEPART(yyyy, DATEADD(m,-1,(#Month+'/1/'+#Year) ))
DECLARE #DiffMonth varchar(2)
set #DiffMonth= DATEPART(mm, DATEADD(m,-1,(#Month+'/1/'+#Year) ))
SELECT T.[Year],
T.[Month]
-- select the sum for each year/month combination using a correlated subquery (each result from the main query causes another data retrieval operation to be run)
,
(SELECT SUM(Stores)
FROM #ABC
WHERE [Year] = T.[Year]
AND [Month] = T.[Month]) AS [Sum_Stores],
(SELECT SUM(SalesStores)
FROM #DEF
WHERE [Year] = T.[Year]
AND [Month] = T.[Month]) AS [Sum_SalesStores],
(SELECT SUM(Products)
FROM #GHI
WHERE [Year] = T.[Year]
AND [Month] = T.[Month]) AS [Sum_Products]
INTO #XYZ
FROM (
-- this selects a list of all possible dates.
SELECT [Year],
[Month]
FROM #ABC --where [Year] = #Year and [Month] = #Month
UNION
SELECT [Year],
[Month]
FROM #DEF --where [Year] = #Year and [Month] = #Month
UNION
SELECT [Year],
[Month]
FROM #GHI --where [Year] = #Year and [Month] = #Month
)
AS T;
SELECT T.[Year],
T.[Month]
-- select the sum for each year/month combination using a correlated subquery (each result from the main query causes another data retrieval operation to be run)
,
(SELECT SUM(Stores)
FROM #ABC
WHERE [Year] = T.[Year]
AND [Month] = T.[Month]) AS [Sum_Stores],
ISNULL((SELECT SUM(Stores)
FROM #ABC
WHERE [Year] = T.[Year]
AND [Month] = T.[Month]),0) - ISNULL((SELECT SUM([Sum_Stores])
FROM #XYZ
WHERE [Year] = #DiffYear
AND [Month] = #DiffMonth),(SELECT SUM(Stores)
FROM #ABC
WHERE [Year] = T.[Year]
AND [Month] = T.[Month])) AS [DIFF_Sum_Stores],
(SELECT SUM(SalesStores)
FROM #DEF
WHERE [Year] = T.[Year]
AND [Month] = T.[Month]) AS [Sum_SalesStores],
ISNULL((SELECT SUM(SalesStores)
FROM #DEF
WHERE [Year] = T.[Year]
AND [Month] = T.[Month]),0) -
ISNULL((SELECT SUM([Sum_SalesStores])
FROM #XYZ
WHERE [Year] = #DiffYear
AND [Month] = #DiffMonth),(SELECT SUM(SalesStores)
FROM #DEF
WHERE [Year] = T.[Year]
AND [Month] = T.[Month])) AS [DIFF_Sum_SalesStores],
(SELECT SUM(Products)
FROM #GHI
WHERE [Year] = T.[Year]
AND [Month] = T.[Month]) AS [Sum_Products],
ISNULL((SELECT SUM(Products)
FROM #GHI
WHERE [Year] = T.[Year]
AND [Month] = T.[Month]),0) -
ISNULL((SELECT SUM([Sum_Products])
FROM #XYZ
WHERE [Year] = #DiffYear
AND [Month] = #DiffMonth),(SELECT SUM(Products)
FROM #GHI
WHERE [Year] = T.[Year]
AND [Month] = T.[Month])) AS [Diff_Sum_Products]
FROM (
-- this selects a list of all possible dates.
SELECT [Year],
[Month]
FROM #ABC where [Year] = #Year and [Month] = #Month
UNION
SELECT [Year],
[Month]
FROM #DEF where [Year] = #Year and [Month] = #Month
UNION
SELECT [Year],
[Month]
FROM #GHI where [Year] = #Year and [Month] = #Month
)
AS T;