First, learn how to use all of the built-in functions of SQL Server/T-SQL because, as with any language, that's where a lot of the performance is.

Second, read and...

The "Levenshtein Distance Algorithm" seems to be one of the most accurate.  Here's one link and, of course, Google is loaded for bear on this subject.

https://www.red-gate.com/simple-talk/sql/t-sql-programming/fuzzy-searches-sql-server/

Thanks for taking the time to write a nice simple article on the subject of LAG.

Shifting gears as a bit of a suggestion...
While a graphical representation of...

No.  It's not...

While you may consider it to be an extra step (and it is), I never import directly into a final table anyway.  I always import into a staging table to...

My favorite job description in an actual ad was one that I found in a newspaper right around 2003.  It was short, sweet, and to the point.

"SQL Wanted:...

I agree with Sue.  You need to fix the permissions on the users of those machines so that can't do such a thing.