I suggest that the calculated column is persisted since the function is deterministic.
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Example for both concatenation functions

-- SQL SERVER 2017...

Suggest you declare the XMLNAMESPACES with a default namespace, makes the query more readable and less error prone.
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USE TEEST;
GO
SET...

Me trying to explain Cartesian produce to my young daughter (failed of course)
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How can I translate this to a 9YSpeak?

Just did a quick test and I'm certain that current identity value is the committed value and the current column value is the uncommitted.
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USE...

I've seen this kind of waits many times, most of the time, the cause is a combination of complex queries with DISTINCT and ORDER BY clauses which would reach half...