$id_tarif=10;  //for examle

while $row < 20 {

$t=sybase_query("select name from tarif_plans where id_plan in (select id_plan from tarif where id_tarif=$id_tarif)",1);

$data_t=sybase_fetch_array($t);
$plan=$data_t[0];

$row++
}
If $row >1, script return zero length page 8-9 times from 10.
Problem is in nested select.