Are you just loading into those 2 tables?  How is the data being loaded?  Can you create a staging table with these constraints already on them, then use SSIS to...

Not sure what the leading decimal is before concat, but the column name should have any effect, even though those columns names are not good.

create table...

No idea what you are asking.  Sounds like homework to me

I would start with the parts that are reaching across databases.  Here's a few:

select top 1 * from CoreHistory..PRODUCT where PRODUCT_ID = c.PRODUCT_ID order by SESSION_ID desc
select...

without any ddl and sample data or an execution plan, we can't help at all.  what performance issues are you having?  How long does it take?

Are there any triggers on the table?

If it's a stored procedure, then either @FYTD_Min and @CYTD_Min are passed in as parameters or looked up somewhere, just don't hardcode them.  You could have them passed with default values (sorta...

without and ddl, sample data and expected results, it will be hard for anyone to help you.

select t.YearMonth,
  t.Department,
  t.CPT,
  t.FSC,
  t.Location,
  t.Units,
  SUM (Units) OVER (ORDER BY CPT, yearMonth, Department, FSC) AS RunningTotal
from #T t

What if you left the table as it is and then add columns to the end as needed?  Not sure why you want to keep the table as close to...

this was triple posted.  I responded to this one

https://www.sqlservercentral.com/Forums/2015379/Query

This is triple posted.  Please use this link as that is where I posted a response

https://www.sqlservercentral.com/Forums/2015379/Query

Duplicate posts are this one and https://www.sqlservercentral.com/Forums/2015382/Need-Specific-result

can you just sum the numbers up 

select DatabaseName,
     sum(ActualSizeMB) as ActualSizeMB,
     sum(MaxRestrictedSizeMB) as MaxRestrictedSizeMB,
     sum(SpaceLeftMB) as SpaceLeftMB
from (
SELECT

I've seen alot  of people (even developers) refer to CSV files as Excel files because they have associated csv extensions with Excel.  Some of the questions the OP asked are...

I was able to get this to return the correct data.  Format File and data file are attached

Here's the sql

...