数据库联合查询输出数量

用tp方法查询班级表，同时在表内输出学生人数

$db_clas = M('clas');

$db_stu = M('stu');

$data_clas = $db_clas->select();

//foreach 循环

foreach($data_clas as $item=>$value){

$count = $db_stu->where('clas_id='.$value['id'])->count();

$data_clas[$item]['count']=$count; //在查询的结果中添加字符段

}

//for 循环

$count =$db_clas->count();

for ($i=0;$i<$count;$i++){

$data[$i]['count']=$db_stu->where(array('clas_id'=>$data[$i]['id']))->count();

}