How to calculate MTD given daily account balance in SQL Server? - sql

Question

I have a table with columns [accountid], [DateEnding], and [AccountBalance].
I need to calculate MTD using the balance of the current month and subtracting the account balance from the last day of the previous month for each accountid.
So far I have this:
SELECT [accountid]
,[DateEnding]
,[AccountBalance]
,[AccountBalance MTD Last] = AccountBalance - FIRST_VALUE(AccountBalance) OVER (PARTITION BY accountid, YEAR(DATEADD(mm,-1,[DateEnding])), MONTH(DATEADD(mm,-1,[DateEnding])) ORDER BY [DateEnding] DESC)
FROM [test]
ORDER BY accountid, DateEnding;

Answer 1

Here, for each distinct account, we find the latest record available according to DateEnding
we then find the last day of the last month by taking a number of days away equal to the current day number. e.g 23rd April 2019 we subtract 23 days to get 1st March 2019
we can then find the balance on that day.
Then put the calculation together in the SELECT
SELECT Q1.accountid,
Q2.DateEnding ,
Q3.EOMbalance,
Q2.LatestBalance,
Q2.LatestBalance - Q3.EOMbalance EOM
FROM (
SELECT Distinct t1.accountid FROM test t1
) Q1
CROSS APPLY (
SELECT TOP 1 t2.AccountBalance LatestBalance, t2.[DateEnding]
FROM test t2
WHERE t2.[accountid] = Q1.accountid
ORDER BY t2.[DateEnding] DESC
) Q2
CROSS APPLY (
SELECT Top 1 t3.AccountBalance EOMbalance
FROM test t3
WHERE t3.[accountid] = Q1.accountid
AND t3.[DateEnding]
= dateadd(day,0 - DAY(q2.dateending), q2.dateending)
ORDER BY t3.[DateEnding] DESC
) Q3

Answer 2

The first answer seems a little complicated for this problem (Cross Apply isn't necessary here).
The following may be easier for you:
I first look at the current day's account balances in subquery 'a'.
Then I look at the account balances from the last day of last month's data, in subquery 'b'.
Then it's just a matter of subtracting the two to show the MTD delta:
select a.accountid,
a.DateEnding,
a.AccountBalance as [Current AccountBalance],
b.AccountBalance as [EOM prior AccountBalance], --added for clarity
a.AccountBalance-b.AccountBalance as [AccountBalance MTD Last]
from
(select accountid, DateEnding, AccountBalance
from #test
where DateEnding = cast(getdate() as date)
/* getdate() returns today's date, so this query will also be with respect to today */
) a
left join
(select *
from #test
where DateEnding = DATEADD(MONTH, DATEDIFF(MONTH, -1, GETDATE())-1, -1)
/*this returns the last day of last month, always*/
) b
on a.accountid = b.accountid
Here is the SQL that makes this sample data and #test table. Simply execute it to have your own '#test' table to run against:
/*drop table #test
drop table #dates */
create table #test ([accountid] varchar(255),[DateEnding] date, [AccountBalance] decimal(16,2))
create table #dates (rnk int,dt date)
insert into #dates (dt)
values (cast('20180101' as date))
DECLARE
#basedate DATE,
#d INT
SELECT
#basedate = '20180101',
#d = 1
WHILE #d < (select datediff(day,cast('20180101' as date),getdate())+2) --select datediff(day,getdate(),cast('20180101' as datetime))
BEGIN
INSERT INTO #dates (dt)
values (DATEADD(day, 1, (select max(dt) from #dates)))
set #d = #d+1
END
update a
set a.rnk = b.rnk
from #dates a
left join (select rank() over (order by dt) rnk,dt from #dates) b on a.dt = b.dt
declare #a int
set #a = 1
declare #i int
set #i = 1
while #a <20
begin
while #i < (select max(rnk) from #dates)
begin
insert into #test
values (#a,(select dt from #dates where rnk = #i),cast(rand()*1000.0+#i as decimal(16,2)))
set #i=#i+1
end
set #a=#a+1
set #i = 1
end