Re: calling a function over several rows

On Tue, Nov 17, 2009 at 1:35 AM, Adam Rich <adam(dot)r(at)sbcglobal(dot)net> wrote:
> Merlin Moncure wrote:
>>
>> On Tue, Nov 17, 2009 at 1:02 AM, Adam Rich <adam(dot)r(at)sbcglobal(dot)net> wrote:
>>>
>>> Hello,
>>> There is an existing function which takes an integer and returns a
>>> record.
>>>  I need to call this function with every integer in a table.  Is there a
>>> simple shortcut for doing this?
>>>
>>> I'm looking for something like:
>>>
>>> select f.*
>>> from function(t.value) f, table t
>>
>> select (f).* from (select function(t.value) as f from table t) q;
>>
>> merlin
>>
>
> Thanks, that's perfect, and much faster than the one I came up with in the
> interim:
>
> select (f(t.value)).* from table t;

Your version is basically correct. It's slower because of a nasty
gotcha that is stemming from the fact that ().* is not really an
operator. It is expanded during parsing so that for each field of
your type, the function is run, like this:

select (f(t.value)).* from table t;
select f(t.value).a, f(t.value).b, f(t.value).c from table t;

I've griped about this a few times, but I don't know if it's fixable
or even broken...it's just something you have to watch out for.

merlin