opération de requête pdo en php

$pdo = new PDO('mysql:dbname=php','root','root');

$sql = "SELECT name,email FROM user WHERE user_id < :user_id";

$stmt = $pdo->prepare($sql);

$user_id = 5;

$stmt->bindParam(':user_id',$user_id,PDO::PARAM_INT);

$stmt->bindValue(':user_id', 6, PDO::PARAM_INT);

$stmt->execute(['user_id'=>5]);

$stmt->setFetchMode(PDO::FETCH_ASSOC);
$row = $stmt->fetch();
$row = $stmt->fetch(PDO::FETCH_ASSOC);
var_export($row); //字符串方式输出
echo &#39;<br>&#39;;
fetch()会将记录指针自动下移
$row = $stmt->fetch(PDO::FETCH_ASSOC);
var_export($row); //字符串方式输出
echo &#39;<hr>&#39;;

while($row=$stmt->fetch(PDO::FETCH_ASSOC)) {
   var_export($row); //字符串方式输出
   echo &#39;<br>&#39;;
}