    public static function exist($tag)
    {
        $tag = Typo::cleanX($tag);
        $sql = "SELECT `name` FROM `cat` WHERE `name` = '{$tag}' AND `type` = 'tag'";
        $q = Db::result($sql);
        // echo Db::$num_rows;
        if (Db::$num_rows > 0) {
            return true;
        } else {
            return false;
        }
    }
The software constructs all or part of an SQL command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended SQL command when it is sent to a downstream component.