CI2.2.6 加载sqlite 能够链接，但是就是查不出表内数据，怎么回事

--------------------------------------------------------------------sqlite 链接配置----------------------------------------------------------------------
$db['sqlite_db']['hostname'] = "sqlite:".realpath(FCPATH . '/db/prov_city.sqlite');
$db['sqlite_db']['username'] = '';
$db['sqlite_db']['password'] = '';
$db['sqlite_db']['database'] = '';
$db['sqlite_db']['dbdriver'] = 'pdo' ;
$db['sqlite_db']['dbprefix'] = '';
$db['sqlite_db']['pconnect'] = TRUE;
$db['sqlite_db']['db_debug'] = TRUE;
$db['sqlite_db']['cache_on'] = FALSE;
$db['sqlite_db']['cachedir'] = '';
$db['sqlite_db']['char_set'] = 'utf8';
$db['sqlite_db']['dbcollat'] = 'utf8_general_ci';
$db['sqlite_db']['swap_pre'] = '';
$db['sqlite_db']['autoinit'] = TRUE;
$db['sqlite_db']['stricton'] = FALSE;
--------------------------------------------------------------------数据查询-------------------------------------
$db = $this->load->database('sqlite_db', TRUE);
$a=$db->query("select * from T_City ");
print_r($a);
------------------------输出结果------------------------------
CI_DB_pdo_result Object
(
[num_rows] => 0
[conn_id] => PDO Object
( )
[result_id] => PDOStatement Object
(
[queryString] => select * from T_City
)
[result_array] => Array
( )
[result_object] => Array
( )
[custom_result_object] => Array
( )

[current_row] => 0
[row_data] =>
)
--------------------------------------------------------------------加入输入错误的表名称 数据查询-------------------------------------
$db = $this->load->database('sqlite_db', TRUE);
$a=$db->query("select * from T_City333 "); //表T_City333 不存在
print_r($a);
会提示数据库错误，表不存在。