Summary fields don't sort by anything. They produce a an aggregate value determined by the context in which they are used.
Create a layout based on the table in which the summary field is defined and the summary field totals values based on the current found set or , if used in a getsummary function or in a sub summary layout part, a subset of the total found set produced by sorting the records into those subsets.
Refer to a summary field in a related table and you get a summary value based on the set of related records.
And then we have a summary field inside a filtered portal which has yet a third context...
That said, a summary report layout based on the table shown first in your layout can produce exactly the results you show at the end--one row for each part-month with a subtotal for both InStock and Comitted. You would sort your records first by SKU, then by month in the same sort records setup. A subsummary layout part or a GetSUmmary function could then be set up with Month as the "break" field to produce the sub totals shown. You'd delete the body layout part to eliminate listing the individual records and just show the sub totals.
There are other options that can be used as well in places where a sub summary layout won't work.
I think I have the report working but how do I get these values to populate into a table?
Why do you need them in the table? This can be done, but may not actually be necessary.
A looping script with GetSummary could be used to copy the sub totals into variables which are then used to create new records in another table.
but there may be other approaches that don't require this.
I believe I mentioned before that these values are a portion of a larger table. They need to be added to already existing records, I was hoping for a calculation or lookup so they would populate automatically. I am not very familiar with scripts. How does a looping script work? Or is there another way to do this?
This is my current overall set up:
Table1 = raw data
Report1 = Based on Table1, Gives me Field summaries by Month and SKU
Table2 = Pulls specific data from Table1 by week for each SKU using Lookups, Needs to also pull data from Report by Month for each SKU
Week1 Week2 Month1 Month2
SKU1 InStock Committed InStock Committed InStock Committed InStock Committed
SKU2 InStock Committed InStock Committed InStock Committed InStock Committed
What is the purpose of Table 2? Why can you not just generate reports based on Table1 instead of having to copy data into Table 2?
Relationships and portals (possibly filtered) can be used to pull up the totals but arranged by SKU with the totals you describe. This is called a 'cross tab' report and you may want to search out threads that discuss that approach.