pdo 连接操作数据库

<?php    
/*
 * 开启pdo，php.ini扩展打开即可
预处理:
    1,?    绑定 $stmt->bindparam("1",$name,PDO::PARAM_STR);  //从1始
    2,:name   $stmt->bindparam(":name",$name);  第三个参数可写可不写
    3,execute(数组);
    如何获得受影响行,插入ID rowCount()   lastInsertId()
 
结果集遍历：4种 
    1,query来foreach   $result = $pdo->query()  可直接foreach $result
    2,bindColumn 绑定列  while($stmt->fetch())
    3,fetch     while($row=$stmt->fetch(PDO::FETCH_ASSOC))
    4,fetchAll  $stmt->fetchall()  返回的是个数组
    如何获取字段[了解]
 */
 
try{
    $dsn = "mysql:host=localhost;dbname=test";   //手册查询
    $pdo = new Pdo($dsn,"root","abc123");  //第四个参数 可初始化设置
    $pdo->query("set names utf8");  //字符集
    $pdo->setAttribute(PDO::ATTR_ERRMODE,PDO::ERRMODE_EXCEPTION);
 
    //字段  select id,username,password from user
    $stmt = $pdo->prepare("desc user");
    $stmt->execute();
    $j = $stmt->columnCount();  //统计列数
     
    for($i=0;$i<$j;$i++){
        echo "<pre>";
        var_dump($stmt->getColumnMeta($i));
        echo "</pre>";
    }
    $stmt->setFetchMode(PDO::FETCH_NUM);
      
    //PDO::FETCH_NUM
    //PDO::FETCH_ASSOC
     
/*  可直接遍历
    $result = $pdo->query("select username,password from user");
    foreach($result as $key=>$value){
        echo $value["username"].$value["password"]."<br>";
    }
 */
/*  execute(数组);  fetchAll  遍历
    $stmt = $pdo->prepare("select username,password from user where id>:id and username=:username");
    $stmt->execute(array(":id"=>120,":username"=>"养生"));  //带不带冒号均可
    $result = $stmt->fetchAll();
    foreach($result as $value){
        echo $value["password"]."<br>";
    }
 */
/*  //:id  fetch遍历
    $stmt = $pdo->prepare("select username,password from user where id>:id");
    $stmt->bindparam(":id",$id,PDO::PARAM_INT);
    $id = 122;
    $result = $stmt->execute();
    while($row = $stmt->fetch()){
        echo $row["username"].$row["password"];
        echo "<br>";
    }
 */
/*  //绑定列 bindcolumn
    $stmt = $pdo->prepare("select username,password from user where id>?");
 
//  $stmt->bindparam("1",$p1,PDO::PARAM_STR);
//  $stmt->bindparam("2",$p2,PDO::PARAM_STR);
    $stmt->bindparam("1",$p3,PDO::PARAM_INT);
 
//  $p1 = "username";
//  $p2 = "password";
    $p3 = 120;
 
    $stmt->execute();
 
    $stmt->bindcolumn("username",$username);
    $stmt->bindcolumn("password",$password);
 
    while($stmt->fetch()){
        echo $username;
        echo $password;
        echo "<br>";
    }
 */
 
}catch(PDOException $e){
    echo $e->getMessage();
}
?>