Does the _function_ 'IF' always evaluate its arguments? or only the two that it is needful to evaluate?
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----- Original Message -----
> From: "Sándor Halász"
>
> Does the _function_ 'IF' always evaluate its arguments? or only the
> two that it is needful to evaluate?
I'm afraid I'm not authoritative on this, but it seems to me that it would =
be very very bad if the third, unused expression were to be evaluated - not=
only from a performance point of view, but who is to say that that express=
ion is not a user-defined function that modifies the database ?
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>>>> 2011/03/14 16:08 +0100, Johan De Meersman >>>>
I'm afraid I'm not authoritative on this, but it seems to me that it would be very very bad if the third, unused expression were to be evaluated - not only from a performance point of view, but who is to say that that expression is not a user-defined function that modifies the database ?
<<<<<<<<
Yes, but Access s "IIF", of the same use, evaluates all three, and the documentation explicitly says so. MySQL s, that I have seen, says neither. Assuming the worst is safer, and then one uses CASE ..., but if not, ....
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> Yes, but Access s "IIF", of the same use, evaluates all three, and the documentation explicitly says so.
Let's be glad we don't depend on Access, then.
PB
-----
On 3/14/2011 7:52 PM, Sándor Halász wrote:
>>>>> 2011/03/14 16:08 +0100, Johan De Meersman>>>>
> I'm afraid I'm not authoritative on this, but it seems to me that it would be very very bad if the third, unused expression were to be evaluated - not only from a performance point of view, but who is to say that that expression is not a user-defined function that modifies the database ?
> <<<<<<<<
> Yes, but Access s "IIF", of the same use, evaluates all three, and the documentation explicitly says so. MySQL s, that I have seen, says neither. Assuming the worst is safer, and then one uses CASE ..., but if not, ....
>
>
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----- Original Message -----
> From: "Sándor Halász"
>
> Yes, but Access s "IIF", of the same use, evaluates all three, and
> the documentation explicitly says so. MySQL s, that I have seen,
> says neither. Assuming the worst is safer, and then one uses CASE
> ..., but if not, ....
Well, they never have been very good at this whole "common sense" thing, ha=
ve they. Sleep with the dog, get bitten by it's lice.
>
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Sy die't drinkt, is eene kwezel
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>-----Original Message-----
>From: Sándor Halász [mailto:hsv@tbbs.net]
>Sent: Monday, March 14, 2011 8:52 PM
>To: Johan De Meersman
>Cc: mysql@lists.mysql.com
>Subject: Re: "IF"
>
>>>>> 2011/03/14 16:08 +0100, Johan De Meersman >>>>
>I'm afraid I'm not authoritative on this, but it seems to me that it would be
>very very bad if the third, unused expression were to be evaluated - not only
>from a performance point of view, but who is to say that that expression is
>not
>a user-defined function that modifies the database ?
><<<<<<<<
>Yes, but Access s "IIF", of the same use, evaluates all three, and the
>documentation explicitly says so. MySQL s, that I have seen, says neither.
>Assuming the worst is safer, and then one uses CASE ..., but if not, ....
>
>
[JS] Also some optimizers (and I don't know if MySQL is that clever) will
figure out which term is the cheapest to evaluate, and will change the order
of evaluation.
Regards,
Jerry Schwartz
Global Information Incorporated
195 Farmington Ave.
Farmington, CT 06032
860.674.8796 / FAX: 860.674.8341
E-mail: jerry@gii.co.jp
Web site: www.the-infoshop.com
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