Re: Libpq: PQftype, PQfsize

 >From: Tom Lane [mailto:tgl@sss.pgh.pa.us] 
>> 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.
>
>Oh ... actually the problem there is that you have the wrong 
>idea about what PQfsize means.  What that returns is 
>pg_type.typlen for the data type, which is always going to be 
>-1 for a varlena type like varchar.
>
>The thing that you need to look at if you want to see 
>information like the max length of a varchar is typmod 
>(PQfmod).  The typmod generally has some funny 
>datatype-specific encoding; for varchar and char it works like this:
>    -1: max length unknown or unspecified
>    n>0: max length is n-4 characters

Thank you very much Tom. PQfmode returns the correct value when using a type
cast, so it solves my current problem. 
Perhaps you will implement the exact column size for querries with character
functions somwhere in the future. It is a nice feature, which is implemented
by Oracle or MS SQL Server.  Do not know about MySQL.

Regards,
Bozena Potempa