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On 10/21/07 17:52, Tom Lane wrote:
> andy <andy@squeakycode.net> writes:
>> I think your comparing apples and oranges. I'll bet that mysql is
>> taking a shortcut and testing the value before updating it.
>
>> The update is probably more close to:
>> update test set name = 'kevin' where passion = 'soccer' and name <> 'kevin';
>
> Yeah, that seems to be what they're doing. PG does not bother to make
> such a test, on the grounds that it would waste more net cycles than it
> would save. Most people are not in the habit of issuing lots of no-op
> updates.
>
> Also, if you have a case where you think that is what will happen, you
> can add the WHERE-condition for yourself; whereas there is no way in
> mysql to get rid of the useless test even if you know it's useless.
Not to bash MySQL (much...) but ISTM that this is another example of
MySQL playing fast and loose with SQL.
IOW, the RDBMS shouldn't try to out-think me even if I seem seem to
be doing something odd.
- --
Ron Johnson, Jr.
Jefferson LA USA
Give a man a fish, and he eats for a day.
Hit him with a fish, and he goes away for good!
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