1:配置数据库(application/config/database.php)修改
$db[‘default‘] = array(
	‘dsn‘	=> ‘‘,
	‘hostname‘ => ‘localhost‘,
	‘username‘ => ‘数据库的用户名‘,
	‘password‘ => ‘数据库密码‘,
	‘database‘ => ‘数据表名‘,
	‘dbdriver‘ => ‘mysqli‘,
	‘dbprefix‘ => ‘‘,
	‘pconnect‘ => TRUE,
	‘db_debug‘ => TRUE,
	‘cache_on‘ => FALSE,
	‘cachedir‘ => ‘‘,
	‘char_set‘ => ‘utf8‘,
	‘dbcollat‘ => ‘utf8_general_ci‘,
	‘swap_pre‘ => ‘‘,
	‘encrypt‘ => FALSE,
	‘compress‘ => FALSE,
	‘stricton‘ => FALSE,
	‘failover‘ => array(),
	‘save_queries‘ => TRUE
);
2:数据库连接($this->load->database());
3:增:
//insert
//语法:$bool=$this->db->insert(‘表名‘,关联数组);
$data=array( ‘username‘=>‘mary‘, ‘password‘=>‘mary‘,//建立一个用户名叫mary,密码为mary的数组,并传递给变量$data ); $bool=$this->db->insert(‘user‘,$data);//将$data插入数据库的user表中 var_dump($bool);//成功则返回TURE
4:删:
//delete
//语法:$bool=$this->db->delete(‘表名‘,WHERE条件); $bool=$this->db->delete(‘user‘,array(‘id‘=>3));//删除数据库.user表里id=3的用户所有信息 var_dump($bool);//成功则返回TURE
5:改:
//update
$data=array(
    ‘password‘=>12345,
);
$bool=$this->db->update(‘user‘,$data,array(‘id‘=>3));//将数据库.user表里id=3的用户密码给为12345
var_dump($bool);//成功则返回TURE
6:查:
//get
$res=$list=$this->db->get(‘user‘);
//var_dump($list);
foreach($res->result() as $item){//利用foreach来列出所有用户名
    echo $item->username;
echo ‘<br />‘;
}
联合查询:
  $this->db->join(‘ci_role‘,‘ci_role.role_id = ci_admin.role_id‘,‘left‘);
					  $query=$this->db->get_where(‘ci_admin‘,array(‘username‘=>$arr[‘username‘],‘pwd‘=>$pwd));
					  $res=$query->result();
原文:http://www.cnblogs.com/gaoxuqing/p/6705017.html