Re: Libpq: PQftype, PQfsize

>From: Tom Lane [mailto:tgl(at)sss(dot)pgh(dot)pa(dot)us]
[..]
>"Bozena Potempa" <Bozena(dot)Potempa(at)otc(dot)pl> writes:
>> I have a test table with varchar(40) column. After executing the
>> following
>> query:
>> select substr(fc,1,2) from test
>> PQftype returns for the result column PG_TYPE_TEXT and
>PQfsize returns -1.
>> Is it the expected behaviour?
>
>Yes. substr() returns text. But even if it returned varchar,
>you'd probably get -1 for the fsize. PG does not make any
>attempt to predict the result width of functions.

Thank you. In this case (substring) there is no much to predict, just a
simple calculation, but I understand that it is a part of larger and more
complicated functionality. I tried to find a workaround with a type cast:
select substr(fc,1,2)::varchar(2) from test
Now the type returned is varchar, but the size is still -1. I think that it
is not a correct return: the size is specified explicitly in the query and
could be used by PQfsize.

Bozena