关于使用PDO连接数据库的一些基本操作

<?php
header("content-type:text/html;charset=utf-8");
$dsn="mysql:dbname=EC_ERP_v2;host=127.0.0.1";
$db_user='WebDev';
$db_pass='WebDev';
try{
$pdo=new PDO($dsn,$db_user,$db_pass);
}catch(PDOException $e){
echo '数据库连接失败'.$e->getMessage();
}
$openid = '94782645F82DCACFa';
$sql="select * from erp_user where user_qq='$openid'; ";
$rmt=$pdo->query($sql);
$res = $rmt->fetchAll();
if(count($res)>0){
echo '用户存在';
echo '<pre>';
var_dump($res);
echo '</pre>';
}else{
$username = 'admin';
$userpsw = md5('123456');
$userheadurl ='http://q.qlogo.cn/qqapp/1404053/94782645F82DCACF41BF9246AEF1';
$time = time();
$sqla = "insert into erp_user (user_name,user_pwd,user_headurl,user_qq,user_createtime) values ('$username','$userpsw','$userheadurl','$openid','$time');";
$rest = $pdo->exec($sqla);
$aa =$pdo->errorInfo();//可以打印错误信息；
var_dump($aa);
echo '影响行数：'.$rest;
}

//新增
$sql="insert into buyer (username,password,email) values ('ff','123456','admin@admin.com')";
$res=$pdo->exec($sql);
echo '影响行数：'.$res;

//修改
$sql="update buyer set username='ff123' where id>3";
$res=$pdo->exec($sql);
echo '影响行数：'.$res;
//查询
$sql="select * from buyer";
$res=$pdo->query($sql);
foreach($res as $row){
echo $row['username'].'<br/>';
}
//删除
$sql="delete from buyer where id>5";
$res=$pdo->exec($sql);
echo '影响行数：'.$res;
?>