codeigniter (CI)是一个优秀、敏捷的PHP开源框架，尤其封装了对数据库的操作，很方便，以下是php ci常用的数据库操作，作个记录：

/* ================================== 查询 $query = $this->db_query("SELECT * FROM table"); ==================================*/ //result() 返回对象数组$data = $query->result(); //result_array() 返回数据 $data = $query->result_array(); //row() 只返回一行对象数组$data = $query->row(); //num_rows() 返回查询结果行数$data = $query->num_rows(); //num_fields() 返回查询请求的字段个数$data = $query->num_fields(); //row_array() 只返回一行数组$data = $query->row_array(); //free_result() 释放当前查询所占用的内存并删除关联资源标识$data = $query->free_result(); /* ================================== 插入操作 ==================================*/ //上次插入操作生成的IDecho $this->db->insert_id(); //写入和更新操作被影响的行数echo $this->db->affected_rows(); //返回指定表的总行数echo $this->db->count_all('table_name'); //输出当前的数据库版本号echo $this->db->version(); //输出当前的数据库平台echo $this->db->platform(); //返回最后运行的查询语句echo $this->db->last_query(); //插入数据，被插入的数据会被自动转换和过滤，例如：//$data = array('name' => $name, 'email' => $email, 'url' => $url);$this->db->insert_string('table_name', $data); /* ================================== 更新操作 ==================================*/ //更新数据，被更新的数据会被自动转换和过滤，例如：//$data = array('name' => $name, 'email' => $email, 'url' => $url);//$where = "author_id = 1 AND status = 'active'";$this->db->update_string('table_name', $data, $where); /* ================================== 选择数据 ==================================*/ //获取表的全部数据$this->db->get('table_name'); //第二个参数为输出条数，第三个参数为开始位置$this->db->get('table_name', 10, 20); //获取数据，第一个参数为表名，第二个为获取条件，第三个为条数$this->db->get_where('table_name', array('id'=>$id), $offset); //select方式获取数据$this->db->select('title, content, date');$data = $this->db->get('table_name'); //获取字段的最大值，第二个参数为别名，相当于max(age) AS nianling$this->db->select_max('age');$this->db->select_max('age', 'nianling'); //获取字段的最小值$this->db->select_min('age');$this->db->select_min('age', 'nianling'); //获取字段的和$this->db->select_sum('age');$this->db->select_sum('age', 'nianling'); //自定义from表$this->db->select('title', content, date');$this->db->from('table_name'); //查询条件 WHERE name = 'Joe' AND title = 'boss' AND status = 'active'$this->db->where('name', $name);$this->db->where('title', $title);$this->db->where('status', $status); //范围查询$this->db->where_in('item1', 'item2');$this->db->where_not_in('item1', 'item2'); //匹配，第三个参数为匹配模式 title LIKE '%match%'$this->db->like('title', 'match', 'before/after/both');$this->db->not_like(); //分组 GROUP BY title, date$this->db->group_by('title', 'date'); //限制条数$this->db->limit(0, 20);