How to two select statements with sum functions in them - mysql

Question

I'm trying to join these two tables and I get an error when I use any join. Union will work but returns all the values in two rows as opposed to 3 which I need. This is what I have so far and what it returns is below it. Any help would be great :)
select C.CustId ,SUM(Ia.Amount) as total
from Invoice I
inner join InvoiceAmtSummary Ia on I.GUIDInvoice=Ia.GUIDInvoice
inner join Customer C on C.GUIDCustomer=I.GUIDCustomer
WHERE DATEPART(mm, I.InvoiceDate) = DATEPART(mm, DATEADD(mm, -1, getdate()))
and DATEPART(yyyy, I.InvoiceDate) = DATEPART(yyyy, DATEADD(yyyy, -0, getdate()))
group by C.CustId
union
select C.CustId ,SUM(Ia.Amount) as total2
from Invoice I
inner join InvoiceAmtSummary Ia on I.GUIDInvoice=Ia.GUIDInvoice
inner join Customer C on C.GUIDCustomer=I.GUIDCustomer
WHERE DATEPART(mm, I.InvoiceDate) = DATEPART(mm, DATEADD(mm, -2, getdate()))
and DATEPART(yyyy, I.InvoiceDate) = DATEPART(yyyy, DATEADD(yyyy, -0, getdate()))
group by C.CustId
The returned result is below with the required result below that
Custid total
a 2
b 9
b 12
c 16
d 3
d 12
Custid total total2
a 2
b 9 12
c 16
d 3 12

Answer 1

select c.custid, c.total, c2.total2
from (select C.CustId ,SUM(Ia.Amount) as total
from Invoice I
inner join InvoiceAmtSummary Ia on I.GUIDInvoice=Ia.GUIDInvoice
inner join Customer C on C.GUIDCustomer=I.GUIDCustomer
WHERE DATEPART(mm, I.InvoiceDate) = DATEPART(mm, DATEADD(mm, -1, getdate()))
and DATEPART(yyyy, I.InvoiceDate) = DATEPART(yyyy, DATEADD(yyyy, -0, getdate()))
group by C.CustId) c
inner join
(select C.CustId ,SUM(Ia.Amount) as total2
from Invoice I
inner join InvoiceAmtSummary Ia on I.GUIDInvoice=Ia.GUIDInvoice
inner join Customer C on C.GUIDCustomer=I.GUIDCustomer
WHERE DATEPART(mm, I.InvoiceDate) = DATEPART(mm, DATEADD(mm, -2, getdate()))
and DATEPART(yyyy, I.InvoiceDate) = DATEPART(yyyy, DATEADD(yyyy, -0, getdate()))
group by C.CustId) c2 on c.custid = c2.custid

Answer 2

I think you are trying to have 2 columns of SUM of different Months. Here is what you can do:
Select C.CustId ,
Sum(Case DATEPART(mm, I.InvoiceDate)
When DATEPART(mm, DATEADD(mm, -1, getdate())) Then Ia.Amount
Else 0 End) As 'Total1',
Sum(Case DATEPART(mm, I.InvoiceDate)
When DATEPART(mm, DATEADD(mm, -2, getdate())) Then Ia.Amount
Else 0 End) As 'Total2'
from Invoice I
inner join InvoiceAmtSummary Ia on I.GUIDInvoice=Ia.GUIDInvoice
inner join Customer C on C.GUIDCustomer=I.GUIDCustomer
WHERE
DATEPART(yyyy, I.InvoiceDate) = DATEPART(yyyy, DATEADD(yyyy, -0, getdate()))
group by C.CustId
I am using Case to avoid the recursive join.

Answer 3

Since you are using MySQL, I would approach by implementing in-line sqlvariables (via my first "from" alias. The #FirstOfThisMonth is computed by subtracting whatever the current day of month is from the current date (less 1).
Ex: Today is April 3rd (3rd day of month). So, -3 = March 31... PLUS 1 brings back to April 1 of current month. Once that date is determined, I can now subtract an entire month for first of PREVIOUS month (March 1st), and subtract 2 months for Feb 1st.
Now that this complexity is done ONCE, we can use these variables instead of constant datepart extraction for month and year. Especially if you consider trying to do two months ago from Feb 10th. (First of current is Feb 1, one month back is Jan 1, two months back is Dec 1 of prior year).
NOW, I simply SUM() based on a case when condition.
if the Invoice Date is >= #TwoMonthsAgo AND LESS THAN #LastMonth, that goes into the two-months-ago total.
the next is Invoice Date >= #LastMonth AND LESS THAN #FirstOfThisMonth for last month's total.
Now, you have a rolling two-month window... If you wanted to go longer, just add another monthly variable reference and SUM() its criteria.
Finally the WHERE clause can only include invoices that are greater or equal to the #TwoMonthsAgo so it doesn't have to go through the entire database
select
C.CustId,
SUM( CASE when I.InvoiceDate >= #TwoMonthsAgo AND I.InvoiceDate < #LastMonth
then Ia.Amount else 0 end ) as TotalTwoMonthsAgo,
SUM( CASE when I.InvoiceDate >= #LastMonth AND I.InvoiceDate < #FirstOfThisMonth
then Ia.Amount else 0 end ) as TotalLastMonth
from
( select #FirstOfThisMonth := date_add( now(), INTERVAL -dayofmonth(now())+1 day ),
#LastMonth := date_add( #myDate, INTERVAL -1 month ),
#TwoMonthsAgo := date_add( #myDate, INTERVAL -2 month )) sqlvars,
Invoice I
inner join InvoiceAmtSummary Ia
on I.GUIDInvoice = Ia.GUIDInvoice
inner join Customer C
on C.GUIDCustomer = I.GUIDCustomer
WHERE
I.InvoiceDate >= #TwoMonthsAgo
AND I.InvoiceDate < #FirstOfThisMonth
group by
C.CustID