[Skimmer]

What version of MySQL are you using? Here's an example for R33 or higher.

PHP код:

CMD:checkplate(playerid, params[])
{
    new plate[128]; // MAX_PLATE_NUMBER
    if (sscanf(params, "s", plate)) return SendClientMessage(playerid, -1, "USAGE: /checkplate (platenumber)");

    new query[128];
    mysql_format(SQL, query, sizeof(query), "SELECT `id` FROM `vehicles` WHERE `plate` = `%e`", plate);

    new Cache:result = mysql_query(SQL, query);

    if (cache_num_rows() > 0)
    {
        // The plate number does exist
    }
    else
    {
        // It doesn't exist
    }

    cache_delete(result);
}