Re: Minor mathematical error in documentation

Tom Lane wrote:
> Russell Smith <mr-russ@pws.com.au> writes:
>
>> In-equality transformations do not guarantee that y > 1.5x == y/x >
>> 1.5.  This is only true for x>0, y < 1.5*x for x<0.  I have not posted a
>> patch as I'm not sure what is the best way to change the example.
>>
>
> Seems a bit nit-picky, but we could change the example to
>
I would agree, it's nit-picky.  But lots of people rely on the truth of
the documentation.  People say I have any y/x > z situation, PostgreSQL
manual says it works better if I do y > z*x.  So they do it, no
questions asked. Which is the real fear from my point of view.
> SELECT ... WHERE x > 0 AND y/x > 1.5;
> becomes
> SELECT ... WHERE CASE WHEN x > 0 THEN y/x > 1.5 ELSE false END;
>
>             regards, tom lane
>
> ---------------------------(end of broadcast)---------------------------
> TIP 9: In versions below 8.0, the planner will ignore your desire to
>        choose an index scan if your joining column's datatypes do not
>        match
>
>