Обсуждение: How can I retrieve a function result?

Luis,

On Mon, Jun 12, 2006 at 06:24:24PM -0500, Luis Alberto Pérez Paz wrote:
> res = PQexecParams ( conn, "select myFunction($1,$2,$3)" , 3, NULL,
> paramValues, paraLenghts, paramFormats, resultFormat);

> It's works fine, however I dont know how can I retrieve the result that
> return the FUNCTION "myFunction". "myFunction" is a postgres FUNCTION which
> returns a INT.

libpq functions for retrieving query results are described here:

http://www.postgresql.org/docs/8.1/static/libpq-exec.html#LIBPQ-EXEC-SELECT-INFO
Have you tried them and do you have a special problem with one of those? If
so, please give more detail.

Getting the result of a function does not differ from getting the result of
a regular select of a table or view.


Joachim

Luis,

On Tue, Jun 13, 2006 at 01:19:32PM -0500, Luis Alberto Pérez Paz wrote:
> The program works fine, actually I can verify that it executes the FUNCTION
> 'myFunction', however I dont know how can I get the return value of the
> FUNCTION 'myFunction' (as you can see in the little example the return
> value can be 0 or -900).

this is similar to retrieving the result of a query that returned one row
and one column. So you just have to use PQgetvalue(res, 0, 0).

Here are a few other examples:

Check if there were rows at all:

        if (PQntuples(res) == 0) {
                /* no rows */
                PQclear(res);
                return (char*) 0;
        }

Check if there was anything else than one column per row:

        if (PQnfields(res) != 1) {
                /* did not get only 1 column back */
                PQclear(res);
                return (char*) 0;
        }

Check whether or not the first column, first row field is NULL:

        if (PQgetisnull(res, 0, 0)) {
                /* got NULL */
                PQclear(res);
                return (char*) 0;
        }

Get the first row, first column value as char*:

        db_value = PQgetvalue(res, 0, 0);


I hope this gives you an idea.

Those functions are in this section of the documentation:

http://www.postgresql.org/docs/8.1/static/libpq-exec.html#LIBPQ-EXEC-SELECT-INFO

Joachim