<?php
$username = $_POST["username"];
$passcode = $_POST["passcode"];
# 一定要mysqli_connect
$con = mysqli_connect("jh.bux.org", "jh", "jhisjh", "mytest");
# 一定要加引号
$sql = "insert into userinfo (username, password) values ('$username', '$passcode');";
mysqli_query($con, $sql);
mysql_close($con);
?>