odbc_fetch_row($...))

[atomix]

...
while (odbc_fetch_row($rec)) {
  $str1 = $str1.odbc_result($rec, "Id");
}

while (odbc_fetch_row($rec)) {
  $str2 = $str2.odbc_result($rec, "Id");
} 

$str1 = "1234", and is correct!
$str2 = ""

How can I use more times odbc_fetch_row() for the same recordset (to have $str2 = "1234" too) ?