Why would you have a dbo.addmonths function when you have a native DATEADD function?

Here's an example with some possible scenarios:

SELECT  SpecialCode,
  CAST(SUBSTRING(SpecialCode, 0, ISNULL( NULLIF(CHARINDEX('/', SpecialCode), 0), 10)) AS int)  AS Expr1,
  CAST(SUBSTRING(SpecialCode, ISNULL( NULLIF(CHARINDEX('/',...

I would start by changing all those SELECT TOP 1. You're reading the tables multiple times when you can read them just once.

Your WHERE clause is not SARGable...

Am I missing something here?
https://www.sqlservercentral.com/Forums/1969990/Advice-help-for-this-query

Have you seen the estimated number of rows? How long would you expect it to take to process 20TB of data?
You should start by filtering the data that you're...

Here's a code sample on how to do it:

WITH cteTable1 AS(
    SELECT col1, col2, SUM(col3) sumcol3, SUM(col4) sumcol4
    FROM Table1
    GROUP BY col1,...