Michael J. Swart has an update for us:
According to Microsoft’s documentation, an UPDATE statement “changes existing data in a table or view”. But what if the values don’t actually change? What if affected rows are “updated” with the original values? Some call these updates non-updating. This leads to a philosophical question: “If an UPDATE statement doesn’t change any column to a different value, has the row been updated?”
I answer yes to that question. I consider all affected rows as “updated” regardless of whether the values are different. I think of the UPDATE statement as more of an OVERWRITE statement. I also think of “affected rows” rather than “changed rows”. In most cases SQL Server thinks along the same lines.
I list some features and areas of SQL Server and whether non-updating updates are treated the same or differently than other updates:
Click through for multiple scenarios and to see whether SQL Server is smart enough to ignore non-updating records in an UPDATE statement.