Re: UPDATE sql question

Ron Johnson <ron(dot)l(dot)johnson(at)cox(dot)net> writes:
>> I'd think that in most cases, the extra time spent checking to see
>> whether the updated columns didn't change would be a net loss.

> Would it always be a net loss, though?

You're asking the wrong question. From my perspective, the question
is whether it'd be a net win averaged across all UPDATEs at all
installations everywhere. I can't believe that it would be.

> CPUs are so fast, nowadays. How many microseconds *would* be spent?

That's been a standard excuse for bad design for decades now :-(. Yeah,
the comparisons might be cheap (or not, on some datatypes) ... but the
potentially-avoided computation is reduced by a faster CPU as well.

If you have a particular application and table where no-op UPDATEs occur
often enough that it's really a win to suppress them, you can put in a
trigger to do it. Or better, fix the application to not issue the
UPDATE in the first place; that saves way more computation for the same
basic comparison overhead.

regards, tom lane