[postgis-users] Is that possible a function to behave differently inside and outside another main function code?

[rodrigosperb]

Hi Kevin,

Thanks for your repply. I can't be sure whether the two functions have the
same X value, and I don't want them twice, that's why I was using UNION,
instead of UNION ALL (which is much faster even...).

But what you said make some sense. Do you think if use first a UNION ALL and
then in the outer query (when I order by q.t) I use DISTINCT may work?

I think I will try it out.

Thanks again for the help.

Rodrigo Sperb



Kevin Neufeld wrote:
> 
> Are you sure you want to use "UNION" and not "UNION ALL"?  The former 
> will remove duplicates, the latter does not.  It's conceivable that when 
> UNIONed, the three SELECT st_X clauses will return a single value.  
> Collected and put through ST_LineFromMultiPoint would probably result in 
> a single point line (depending on which version of PostGIS you are using 
> - the newer versions will ERROR with "geometry requires more points").
> 
> Hope that helps,
> Kevin
> 
> rodrigosperb wrote:
>> Hello,
>>
>> I have a bit of a problem that is sort of driving me crazy. I need to
>> perform an "addition of two (mathematical) functions". I represent them
>> as
>> linestrings in my solution, and it is part of another bigger function.
>> The
>> code is as follows:
>>
>> ...header...
>> SELECT st_LineFromMultiPoint(st_Collect(st_MakePoint(xy.t,xy.at)))
>> FROM (SELECT q.t, dr_delay_value($1,q.t) +
>> dr_delay_value($3,dr_delay_value($1,q.t)) AS at
>>       FROM (SELECT st_X(st_PointN($1,n)) AS t
>> 	    FROM generate_series(1,st_NumPoints($1)) AS h(n)
>> 	    UNION
>> 	    SELECT st_X(st_PointN($2,n)) AS t
>> 	    FROM generate_series(1,st_NumPoints($2)) AS h(n)
>> 	    UNION
>> 	    SELECT st_Xmax($1) AS t
>>             ) AS q ORDER BY q.t) AS xy
>> ...bottom...
>> dr_delay_value() is simply a look-up function that takes the Y value for
>> a
>> certain X.
>>
>> The thing is that eventually this fuction is failing on returning more
>> specifically a 2-points linestring (that sould) and returns only a single
>> point one. Now, I have prepared a "wrapper" PL/Pgsql function to keep
>> track
>> of what is passed to that function (perhaps that was the reason for the
>> error. With that I'm pretty much sure that the arguments passed are fine,
>> and still get the same error... Strangely, with my wrapper function
>> keeping
>> track of the arguments passed to the function I was able to try out to
>> run
>> the same request (that inside of the bigger function fails) separately,
>> and
>> guess what? is simply works!!
>>
>> I hope anyone may have a clue of what is going on. That's a very strange
>> behavior, I would say.
>>
>> Regards,
>>
>> Rodrigo Sperb
>>   
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