recreate global temporary table gtt(id int) on commit delete rows;
commit;

execute block as
declare n int = 1000000;
declare i int = 0;
begin
    while( i < n) do begin
        i = i + 1;
        delete from gtt;
        insert into gtt(id) values(:i);
    end
end

@echo off
echo before   connect: %time%
echo quit;>tmp.tmp
isql 192.168.0.220/3333:oltp30 -pag 0 -i tmp.tmp
del tmp.tmp 2>nul
echo after disconnect: %time%

execute block as
declare n int = 10000; --0000;
declare i int = 0;
begin
  delete from gtt;
  insert into gtt(id) values(:i);
  while( i < n) do begin
    i = i + 1;
    update gtt set id=:i;
  end
end