Summing Two Columns from Two Tables with Two Dates - sql

Question

I work for a CPG company and need to create a report that compares the previous month's delivered units to the next month's forecast. (Simply, our forecasting tool screws up occasionally and this will help identify when the forecast is off.)
My issue is my SQL query is summing forecast sales correctly, but the sum of total delivered is not respecting the dates I have in my WHERE clause -- it's summing total delivered for as far back as the query can reach.
Here is my query:
SELECT
DelUnits.Customer, DelUnits.ObsText01,
FinalFcst.SKU, FinalFcst.Customer,
SUM(DelUnits.Value) AS TotalDelivered,
SUM(FinalFcst.FinalFcst) AS ForecastSales
FROM
DelUnits
LEFT JOIN
FinalFcst ON DelUnits.Customer = FinalFcst.Customer
WHERE
(FinalFcst.DT >= '2018-01-01' and FinalFcst.DT <= '2018-01-31')
AND (DelUnits.Date >= '2017-12-01' and DelUnits.Date <= '2017-12-31')
AND DelUnits.ObsText01 = '10_LB'
AND FinalFcst.SKU = '10_LB'
GROUP BY
DelUnits.Customer, DelUnits.ObsText01, FinalFcst.SKU, FinalFcst.Customer
Again, the query seems to work correctly for the final forecast (summing the forecast between 1/1/18 - 1/31/18) but sums the entire delivery history for a customer. I don't understand why it won't sum the delivery history for just 12/1/17 - 12/31/17.
Thank you for your help!

Answer 1

Presumably, there is only one row for FinalFcst. So, either include it in the GROUP BY clause or use MAX() instead of SUM():
max(FinalFcst.FinalFcst) as ForecastSales

Answer 2

One way to achieve this is to calculate TotalDelivered and ForecastSales in 2 different queries and then join them together.
Try this:
SELECT DelUnits.customer,
DelUnits.obstext01,
FinalFcst.sku,
FinalFcst.customer,
totaldelivered,
forecastsales
FROM (SELECT customer,
obstext01,
Sum(value) AS TotalDelivered
FROM delunits
WHERE date >= '2017-12-01'
AND date <= '2017-12-31'
AND obstext01 = '10_LB'
GROUP BY customer,
obstext01) DelUnits
LEFT JOIN (SELECT customer,
sku,
Sum(finalfcst) AS ForecastSales
FROM finalfcst
WHERE dt >= '2018-01-01'
AND dt <= '2018-01-31'
AND sku = '10_LB'
GROUP BY customer,
sku) FinalFcst ON DelUnits.customer = FinalFcst.customer

Answer 3

You have a many to many relationship between the tables. Ultimately you need to SUM() one table before joining to the other to create a one to many relationship, or you end up duplicating records.
My favorite approach is a derived table:
SELECT C.Customer,
C.ObsText01,
FC.SKU,
C.TotalDelivered,
SUM(FC.FinalFcst) ForecastSales
FROM (SELECT SUM(Value) TotalDelivered, Customer, ObsText01
FROM DelUnits
WHERE Date >= '2017-12-01' AND Date <= '2017-12-31'
AND ObsText01 = '10_LB'
GROUP BY Customer) C
LEFT JOIN FinalFcst FC ON C.Customer = FC.Customer
AND FC.DT >= '2018-01-01'
AND FC.DT <= '2018-01-31'
AND FC.SKU = '10_LB'
GROUP BY C.Customer, C.ObsText01, FC.SKU, C.TotalDelivered
A couple things: Added your forecast table filters to the join predicate, since having those in the WHERE will create an INNER JOIN out of your LEFT JOIN. Also removed FC.Customer from the select and the group since it is redundant with C.Customer.

Answer 4

Maybe you could try to create a temp table to calculate the delivery history. I am not sure of the SQL Server verbiage, but something like this:
WITH DEL_HIST AS
(SELECT DelUnits.Customer,
DelUnits.ObsText01,
sum(DelUnits.Value) as TotalDelivered,
FROM DelUnits
Where(DelUnits.Date >= '2017-12-01' and DelUnits.Date <= '2017-12-31')
and DelUnits.ObsText01 = '10_LB'
Group By DelUnits.Customer, DelUnits.ObsText01)
SELECT
DEL_HIST.Customer,
DEL_HIST.ObsText01,
FinalFcst.SKU,
FinalFcst.Customer,
DEL_HIST.TotalDelivered,
sum(FinalFcst.FinalFcst) as ForecastSales
FROM DEL_HIST
left join FinalFcst ON DelUnits.Customer = FinalFcst.Customer
Where (FinalFcst.DT >= '2018-01-01' and FinalFcst.DT <= '2018-01-31')
and FinalFcst.SKU = '10_LB'
Group By DelUnits.Customer, DelUnits.ObsText01, FinalFcst.SKU, FinalFcst.Customer