Did you test that code? It doesn't run:
Msg 207, Level 16, State 1, Line 11
Invalid column name 'Schedule'.
Msg 207, Level 16, State 1, Line...

You can't set a list of values to a variable. If you want to do something for each Case ID, you'll likely need to use a cursor, and allocate the...

Question, what is the following trying to achieve?DECLARE @CaseID nvarchar(10) = (select cast(CaseID as nvarchar(10)) from [MainDB].[dbo].[AllCases] )
Does your table, AllCases, only have one...

This is untested, as you didn't provide DDL and consumable data, but:
SELECT *
FROM #Master M
  CROSS APPLY dbo.DelimitedSplit8K(M.Schedule, ',') DS
  LEFT JOIN...

Personally, I would create my query, something like below, and then use my presentation layer (SSRS & a matrix, Excel & a pivot table, for example), and pivot the data.

Sorry, in my own haste:
USE sanroque;
GO

UPDATE dbo.Inventory
SET Price = T2.Price
FROM farwest.dbo.Inventory T2
WHERE T2.ItemNum = Inventory.ItemNum;

It's probably not the destination but the source. ACE is a "wonferful" thing. What length does the source have to
For your URL column and what is the longest length...

A few minutes would have been nice 😉

The error is telling you that you're trying...

Just like a normal join and update statement:
Update MyTable1
SET MyColumn1 = (SELECT T2.MyColumn2
      FROM DB2.dbo.MyTable2 T2
      WHERE T2.MyID = MyTable1.MyID);

Found it: https://www.sqlservercentral.com/Forums/1836905/Cascading-Parameters-first-choice-determines-dataset-used-for-next-drop-down-How