Are you creating a temp table i.e. one that begins with a hash (#) or are you using a permanent table name?

Yes, that's a bit shorter and generally more efficient. I'm wondering if there were a lot more that 12 items per customer and the right indexes on the...

;WITH CTE AS
(
    SELECT DISTINCT CustomerCode
      FROM myTable
)
SELECT B.*
  FROM CTE A
 CROSS APPLY(SELECT TOP(12) *
...

;WITH CTE AS
(
    SELECT DISTINCT CustomerCode
      FROM myTable
)
SELECT B.*
  FROM CTE A
 CROSS APPLY(SELECT TOP(12) *
  ...

If you are sure you always want it to seek the values you can give the query a hint:

SELECT *
  INTO #SROISDPL
 ...

You need a colon after numbers:

def calculate_sum(numbers):
    total = 0
    for num in numbers:
       ...

As Jeff said partitioning is the best way and fastest way to remove large chucks of data by date.

When you want to regularly remove old data from a database, there...

Paste it into Excel and create a line chart then add a trend line.

Here is something to get you started:

WITH CompanyData AS 
(
    SELECT * FROM (VALUES
        ('[24]7 Customer, Inc.'),
...

The code was not created by me. I am just investing some one else's code, this person is leaving us soon. I just want to make sure that the...

Have you checked it returns the same results?

You are thinking LEFT JOIN works like OUTER APPLY (it doesn't). You can rewrite the first query using OUTER APPLY instead of LEFT JOIN:

SELECT Grades.[Name] AS Grade,
...

I asked ChatGPT:

WITH RankedEmployees AS (
  SELECT
    employee_id,
    employee_name,
    department,
    joining_date,
   ...

This appears to be a classic "Next_ID" table and I find it difficult to understand why anyone would be using such a thing in this day and age, especially...

I would indent the query like this:

FROM CHG
LEFT JOIN CAMCHARG CC  
     LEFT JOIN CAMRULE CR    
  ...