hostname: 127.0.0.1
  port：3306
  user： (注册名)
  password:   
  database: c9 (cloud9数据库自带的)

  $ mysql-ctl install;   //安装mysql数据库，已经安装则不需要执行本语句
  
  $ mysql-ctl start;  //启动mysql. 第一次启动时会创建一个空数据库
  
  $ mysql-ctl cli;    // run the MySQL interactive shell 运行进入交互式shell脚本
  mysql>  show databases; //显示mysql中拥有的数据库 执行 cli 后会进入 mysql> 
  mysql>  create database phptest;  //新建名字为phptest的数据库
  mysql>  use phptest;   //使用phptest数据库
  mysql>  show tables;   //显示数据库中的表
  SHOW VARIABLES WHERE Variable_name = 'hostname';  //得到hostname

  <?php
 $con = mysqli_connect("127.0.0.1","用户名","密码","w3cPhpdb");//""代表密码为空，"w3cPhpdb"是数据库名
  if (!$con)
   {
        die('Could not connect: ' . mysql_error());
   }
     echo "Connected successfully";
  $query = "SELECT * FROM users";
  $result = mysqli_query($con, $query);
   while ($row = mysqli_fetch_assoc($result)) {
          echo "The ID is: " . $row['id'] . " and the Username is: " . $row['username'];
  }
  ?>
  
  ------------------------------------------------------------
  
  <?php
  $conn = new mysqli("127.0.0.1","a3zhangsen","","w3cPhpdb");//""代表密码为空，"w3cPhpdb"是数据库名
  if ($conn->connect_error) {
        die("Connection failed: " . $conn->connect_error);
  } 
  $sql = "SELECT id,username FROM users";
  $result = $conn->query($sql);
  if ($result->num_rows > 0) {
      // 输出每行数据
         while($row = $result->fetch_assoc()) {
        echo "<br> id: ". $row["id"]. " - Name: ". $row["username"]."<br>";
    }
 } else {
    echo "0 results";
  }
  $conn->close();

  (3)包括Step 1: Setup MySQL on Cloud 9 (配置MySQL)
         Step 2: Create a test database (创建一个测试用数据库)
         Step 3：Get the credentials you'll need to connect to the database from PHP.
         得到连接php数据库需要的凭证：如 user ,password ,hostname.
         last Step:在php文件中连接mysql数据库。(该链接的这个方法不知名原因失败，可使用上面3 的方法)

$ mysql-ctl install

MySQL 5.5 database added.  Please make note of these credentials:
Root User: username
Database Name: c9

$ mysql-ctl cli

        Welcome to the MySQL monitor.  Commands end with ; or \g.
        Your MySQL connection id is 24
        Server version: 5.5.37-0ubuntu0.14.04.1 (Ubuntu)

mysql>  show databases;
  +--------------------+
  | Database           |
  +--------------------+
  | information_schema |
  | c9                 |
  | mysql              |
  | performance_schema |
  +--------------------+
  4 rows in set (0.15 sec)

        标签： 数据库 的 数据表 杂谈	
        MySQL数据库查看数据库 数据表的命令。
        进入MySQL Command line client下查看当前使用的数据库:
         mysql>select database();
        
         mysql>status;
        
         mysql>show tables;
        
         mysql>show databases;  //可以查看有哪些数据库,返回数据库名(databaseName)
         
        mysql>use databaseName;  //更换当前使用的数据库
        
         mysql>show tables;  //返回当前数据库下的所有表的名称
        
         或者也可以直接用以下命令
         mysql>show tables from databaseName; //databaseName可以用show databases得来
        
         mysql查看表结构命令，如下:
         desc 表名;
         show columns from 表名;
        
         或者 
         describe 表名;
         show create table 表名;
       
         或者  
         use information_schemaselect * from columns where table_name='表名';
        
         查看警告:
         mysql> show warnings;
         Rows matched: 1 Changed: 0 Warnings: 1

           +---------+------+-------------------------------------------+
           | Level | Code | Message |
           +---------+------+-------------------------------------------+
           | Warning | 1265 | Data truncated for column 'name' at row 3 |
           +---------+------+-------------------------------------------+
           1 row in set