Bulant Denys wrote:
> --- Michael Stassen <Michael.Stassen@stripped> a
> écrit :
>
>>denys wrote:
>>
>> > SELECT country
>> > FROM Rates
>> > WHERE fieldvalue1 <> 0 AND fieldvalue2 <> 0 AND
>>fieldvalue3 <> 0
>> > ORDER BY country
>> > is it what you want ?
>> >
>>
>>Gleb Paharenko wrote:
>>
>>
>>>Hello
>>>
>>>You may use query like this:
>>> select country from rates where (fieldvalue1 !=0)
>>
>>and (fieldvalue2 !=0)
>>
>>> and (fieldvalue3 !=0) order by country;
>>>
>>>See:
>>>
>>
> http://dev.mysql.com/doc/mysql/en/Comparison_Operators.html
>
>>And since 0 is false and every other number is true,
>>this could be
>>simplified to
>>
>> SELECT country
>> FROM Rates
>> WHERE fieldvalue1 AND fieldvalue2 AND fieldvalue3
>> ORDER BY country;
>>
>>Michael
>>
> I will go to bed less fool this evening... Is it just
> a clearest way to write it, or is there some
> performance issues too ?
In theory, "fieldvalueN != 0" causes a comparison operation which will
return 1 or 0 (true or false) for each field, then the results are combined
with ANDs, which would be 3 extra comparisons compared to simply combining
with ANDs. In practice, I'd bet the optimizer is smarter than that, and the
performance will be identical. Even if the "extra" comparison were not
optimized away, I doubt it would appreciably affect the speed. You could
certainly try it both ways with your data to see if if you get any
difference, but I don't expect any.
Michael
