Defensive database programming: fun with UPDATE.

It is well known that UPDATE ... FROM command does not detect ambiguities. Also it well known that ANSI standard UPDATE may perform very poorly and may be difficult to maintain, because it does not adhere to the fundamental DRY (Don't Repeat Yourself) principle. I will tweak UPDATE ... FROM in three different ways so that you can detect or handle ambiguities without having to repeat one and the same subquery over and over again. Prerequisites The following tables and sample data are used in this...(read more)

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