firebird>isql
Use CONNECT or CREATE DATABASE to specify a database
SQL> set sql dialect 1;
SQL> create database 's:\temp\1.fdb';
SQL>
SQL> select round(0.001*623.20,3) as TMP from rdb$database;

                    TMP
=======================
     0.6230000000000000

SQL> select round(0.001*623.20,4) as TMP from rdb$database;

                    TMP
=======================
     0.6232000000000000

SQL> set sql dialect 1;
SQL> create database 's:\temp\1.fdb';
SQL> select TMP,
CON> cast(TMP as varchar(10)) from
CON> (select round(0.001*623.20,2) as TMP from rdb$database);

                    TMP CAST
======================= ==========
     0.6200000000000000 0.62