$list = mysqli_connect('localhost','root','root');
mysqli_select_db($list,'yi_duo');
mysqli_query($list,'set names utf8');
$ser = 'select * from yi_yi inner join yi_er where yi_yi.info_id=yi_er.id';
$res= mysqli_query($list,$ser);
$ass = mysqli_fetch_assoc($res);
$ser = 'SELECT
ymt_ming.xing,ymt_jiaoshi.laoshi,ymt_chor.username
FROM
ymt_ming
INNER JOIN
ymt_jiaoshi
ON
ymt_ming.jiaoshi_id=ymt_jiaoshi.id
INNER JOIN
ymt_chor
ON
ymt_ming.chor_id=ymt_chor.id
';
$res= mysqli_query($list,$ser);
while($ass = mysqli_fetch_assoc($res)){
print_r($ass);
echo "<br>";
}