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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