$sql="select sess_value from sess where sess_id='$sess_id'";
$rs=mysqli_query($link,$sql);
$rows=mysqli_fetch_row($rs);
return (string)$rows[0];
}
//写入会话
function write($sess_id,$sess_value) {
global $link;
$sql="insert into sess values ('$sess_id','$sess_value',unix_timestamp()) on duplicate key update sess_value='$sess_value',sess_time=unix_timestamp()";