A text key can look the same to a person and still fail a join. Capitalization and leading spaces are common causes. LOWER and TRIM produce a consistent comparison key, but keep the original value when someone needs to trace a mismatch back to its source. A cleanup rule should follow the business definition rather than silently rewriting every text column.
SPLIT_PART reads one part of a delimited string; email domains provide a small example. Missing input remains missing unless you deliberately replace it. TRY_TO_NUMBER is useful for imported text because a bad value returns NULL instead of stopping the query. Count failed conversions separately before accepting the cleaned data into a report.