连接数据库的过程

<?php
  //1.创建数据库连接
    //$连接变量 = mysqli_connect("地址","数据库用户名","密码","数据库","端口");
  $con = mysqli_connect("localhost","root","123456","test","3306");
//2.判断是否连接成功
  if (!$con){
    //如果连接不成功，则提示失败提示
    die('Could not connect: ' . mysql_error());
    //如果连接成功，则执行代码
  }else{
    //设置字符集
    mysqli_set_charset($con,'utf8');
    //3.执行SQL语句，如增删改查
    //$结果 = mysqli_query(连接变量,SQL语句)
    $result = mysqli_query(
      $con,
      "SELECT * FROM `user`"
    );
    //4.设置请求头，否则跨域会请求不成功
    header('Access-Control-Allow-Origin:*');
    //5.输出数据，以json的方式
    echo json_encode(mysqli_fetch_all($result),JSON_UNESCAPED_UNICODE);
  };
    //6.关闭连接
  mysqli_close($con);
?>