<?php
$db = sqlite_open("/path/to/database");

while (1) {
    $ses_id = md5(mt_rand());
    if (@sqlite_query("INSERT INTO session_table (ses_id) VALUES('".$ses_id."')", $db)) {
        // success, unique session generated
        break;
    }
    $errno = sqlite_last_error($db);
    if ($errno != SQLITE_CONSTRAINT) {
        // some error (not duplicate key) occurred
        die(sqlite_error_string($errno));
    }
}
?>