Re: Problem on PostgreSQL (error code, store procedures)

> 
> I would like to know if there are any global variables
> storing the error code or the number of rows affected
> after each execution of the SQL statement.

You did not mention which interface you are using. 
In C there are functions available like extern const char *PQcmdTuples(PGresult *res);to learn about the rows affected or extern int	PQntuples(PGresult *res);to learn about the number of rows found (SELECT) or extern ExecStatusType PQresultStatus(PGresult *res);to learn about the status of the SQL command. 
Unfortunately, there are no error codes at all. 
In PL/pgSQL (which I do not use) I've found GET DIAGNOSTICS variable = ROW_COUNT ; refer to plpgsql-statements.html 

> 
> Also, for Postgresql function, I have checked that I
> can only call the function by: select function(parms)
> or by EXECUTE PROCEDURE function(parms) in the trigger
> action. I wonder whether there is any other method for
> calling the function which is similar to the stored
> procedures in the MS SQL server?

I'm afraid NO. 

Regards, Christoph