php中使用PDO预编译查找结果集返回为空数组

header("content-type: text/html; charset=utf-8");

$dsn = "mysql:host=localhost; port= 3306;dbname=test;charset=utf8";

$username = "root";

$password = "12345";

$pdo = new PDO($dsn,$username,$password);

//设置错误处理模式为异常模式

$pdo->setAttribute(PDO::ATTR_ERRMODE,PDO::ERRMODE_EXCEPTION);

//构建预编译SQL语句

$sql = "select * from student where (salary between ? and ?) and edu in ( ? )";

//预编译SQL语句，返回结果集

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

$PDOStatement->bindValue(1,"10000");

$PDOStatement->bindValue(2,"20000");

$PDOStatement->bindValue(3,"'大专','本科','研究生'");

$PDOStatement->execute();

$rows = $PDOStatement->fetchAll(PDO::FETCH_ASSOC);

print_r($rows);



//抛出异常并捕获错误信息

try{

   

}catch(PDOExcepton $error){

    echo "错误状态码".$error->getCode();

    echo "
错误状态码".$error->getCode();

    echo "
错误行号".$error->getLine();

    echo "
错误错误文件".$error->getFile();

    echo "
错误信息".$error->getMessage();

}