codeigniter中DB类的用法收集

链接数据库 
------- 
$this->load->database();//手动连接数据库 
//连接多数据库 
$DB1 = $this->load->database('group_one', TRUE); 
$DB2 = $this->load->database('group_two', TRUE); 

查询 
------- 
//参数绑定形式 
$sql = "SELECT * FROM some_table WHERE id = ? AND status = ? AND author = ?"; 
$this->db->query($sql, array(3, 'live', 'Rick')); 
//多结果标准查询 
$query = $this->db->query($sql); //自定义 
$query = $this->db->get('tablename'); //便捷形式，相当于:SELECT * FROM tablename 
$query = $this->db->get('tablename', 10, 20); // 相当于: SELECT * FROM tablename LIMIT 20, 10 
$query->result() //对象形式 
$query->result_array() //数组形式 
 
$query->num_rows() //总条数 
$query->num_fields() //字段数 
//单结果标准查询 
$row = $query->row(); //对象形式 
$row = $query->row_array(); //数组形式 
 
插入 
------- 
$data = array( 
 'title' => $title, 
 'name' => $name 
 ); 
$this->db->insert('tablename', $data); //便捷插入 
$this->db->insert_string('tablename', $data);  //便捷插入 
$this->db->insert_id() //刚插入的id 
$this->db->affected_rows() //影响的行数(update,insert) 

更新 
------- 
$data = array( 
   'name' => $name, 
   'email' => $email 
   ); 
$where = "id = 1"; 
$this->db->update('tablename', $data); 
$this->db->update_string('tablename', $data, $where); 

删除 
------- 
$array = array( 
  'name' => $name, 
  'title' => $title 
   ); 
$this->db->delete('tablename', $array); 
// Produces: 
// "DELETE FROM tablename WHERE name = '$name' AND title = '$title'" 
$this->db->truncate('tablename'); //清空表 
// Produce: TRUNCATE tablename 

（where） 
------- 
$array = array( 
   'name' => $name, 
   'title' => $title 
   ); 
$this->db->where($array); 
// Produces: "WHERE name = '$name' AND title = '$title'" 
----------------------------------------------------- 
$this->db->count_all('tablename'); //表中记录总行数 
----------------------------------------------------- 
$query->free_result() //释放资源