Codeigniter中的数据库错误1146

I am using Codeigniter framework to build a website. I am receiving this error:

Error Number: 1146
Table 'users.ci_sessions' doesn't exist

SELECT `data` FROM `ci_sessions` WHERE `id` = '5e47bcb40c2954bd7329ff3fbcf253007a0563cc'

Filename: libraries/Session/drivers/Session_database_driver.php
Line Number: 166

Here is how session is defined: In config.php:

$config['sess_driver'] = 'files';
$config['sess_cookie_name'] = 'ci_session';
$config['sess_table_name'] = 'ci_sessions';
$config['sess_expiration'] = 7200;
$config['sess_save_path'] = NULL;
$config['sess_match_ip'] = FALSE;
$config['sess_time_to_update'] = 300;
$config['sess_regenerate_destroy'] = FALSE;
$config['sess_encrypt_cookie']  = FALSE;
$config['sess_use_database']    = FALSE;
$config['sess_driver'] = 'database';       // changed from file
$config['sess_save_path'] = 'ci_sessions'; // table name
//$config['sess_save_path'] = sys_get_temp_dir();
$config['sess_match_ip']        = FALSE;
$config['sess_match_useragent'] = TRUE;
$config['sess_time_to_update']  = 300;
$config['sess_use_database'] = TRUE;

In autoload.php:

$autoload['libraries'] = array('database','session');

I have read https://ellislab.com/codeigniter/user-guide/libraries/sessions.html and followed all steps to properly access the session. Any suggestion on how to fix above error?

Actually you are mixing up both session drivers i.e database and file, so if you would like to use file driver read here the official documentation: http://www.codeigniter.com/userguide3/libraries/sessions.html#files-driver

And if you want to use database driver: http://www.codeigniter.com/userguide3/libraries/sessions.html#database-driver

Also i had encounter an strange bug in auto loading libraries.

Please add session driver before database driver in autoload array as:

$autoload['libraries'] = array('session','database');

1. Note that the user-guide you've linked to is for version 2.2.0 and no longer official, while you're using 3.0.x.
2. Read the actual user guide here: http://www.codeigniter.com/userguide3/libraries/sessions.html
3. Don't just tell us that you've read and followed all steps, but actually do it - you haven't created a ci_sessions table in the database. The error message itself tells you this.

be careful with these parameters in config.php

$config['sess_driver'] = 'database';
$config['sess_cookie_name'] = 'ci_session'; //ci_session don't add 's' in last
$config['sess_expiration'] = 7200;
$config['sess_save_path'] = 'ci_sessions'; //ci_sessions add 's' in last
$config['sess_match_ip'] = FALSE;
$config['sess_time_to_update'] = 300;
$config['sess_regenerate_destroy'] = FALSE;