$this->db->select();  //選擇查詢的字段
$this->db->select_max();
$this->db->select_min();
$this->db->select_avg();
$this->db->select_sum();
$this->db->from();   //選擇表名
$this->db->join();
$this->db->get();   //得到查詢結果
$this->db->get_where();
$this->db->where();
$this->db->or_where();
$this->db->where_in();
$this->db->or_where_in();
$this->db->where_not_in();
$this->db->or_where_not_in();
$this->db->like();
$this->db->or_like();
$this->db->not_like();
$this->db->or_not_like();
$this->db->group_by();
$this->db->distinct();
$this->db->having();
$this->db->or_having();
$this->db->order_by();
$this->db->limit();
$this->db->count_all_results();

$this->db->insert();

$this->db->set();
$this->db->update();

$this->db->delete();

$this->db->empty_table();
$this->db->truncate();

$this->db->start_cache()
$this->db->stop_cache()
$this->db->flush_cache()

result()  //返回對象數(shù)組
result_array() //返回二維數(shù)組
row()   //返回一個對象
row_array()  //返回一維數(shù)組
num_rows()  //返回查詢的行數(shù)
num_fields() //返回查詢結果的字段數(shù)
free_result() //釋放查詢所占的資源內(nèi)存

$this->db->insert_id()  //獲取剛剛插入的id
$this->db->affected_rows() //修改或插入影響的行數(shù)
$this->db->count_all();  //統(tǒng)計記錄的總條數(shù) 這一函數(shù)加入where條件無效
$this->db->last_query();  //最后一條執(zhí)行的sql語句
//注意以下兩個函數(shù)僅返回sql語句 不執(zhí)行sql語句
$data = array('name' => $name, 'email' => $email, 'url' => $url);
$str = $this->db->insert_string('table_name', $data);
$data = array('name' => $name, 'email' => $email, 'url' => $url);
$where = "author_id = 1 AND status = 'active'";
$str = $this->db->update_string('table_name', $data, $where); //返回正確格式的更新字符串