SQLite3查询失败

Question

SQLite3查询失败。在数据库中插入数据确定，但没有得到数据，我的错是什么？

protected function db2Array($data)
{
    $arr = array();
    while ($row = $data -> fetchArray(\SQLITE3_ASSOC))
    {
        $arr[] = $row;
    }
    return $arr;
}

function getNews()
{
    try
    {
        $sql = "SELECT msgs.id as id, 
                       title, 
                       category.name as category, 
                       description, 
                       source, 
                       datetime
                  FROM msgs,
                       category
                 WHERE category.id = msgs.category
              ORDER BY msgs.id DESC";
        $res = $this->_db -> query($sql);
        if(!is_object($res))
        {
            throw new Exception ($this->_db -> LastErrorMsg());
        }
        return $this->db2Array($res);
    }
    catch (Exception $exs)
    {
        //$exs -> getMessage();
        return FALSE;
    }
}

此代码返回：array（size = 0）empty