php - 如果php中的数据库查询没有返回结果，如何显示消息

Question

想知道是否有人可以提供帮助。我正在运行有关 php 和 mysql 的教程，其中有一个笑话数据库，其中包含:

• 笑话表中的笑话
• 作者表中的作者
• 类别表中的类别

我有一个名为authors.html.php 的页面，其中包含作者列表，其中包含添加作者、编辑/删除作者的选项(位于每个返回作者的姓名旁边)。我想做的是，如果包含作者的数据库为空，而不是显示以下 php 错误:

Notice: Undefined variable: authors in C:\wamp\www\chapter7\admin\authors\authors.html.php on line 22

我想显示一条简洁的消息，表示未找到结果。

我的代码如下:

<?php   
  include $_SERVER['DOCUMENT_ROOT'] . '/chapter7/includes/db.inc.php';
    try {
            $result = $pdo->query('SELECT id, name FROM author');
    } catch (PDOException $e) {
            $error = 'Error fetching authors from the database!';
            include $_SERVER['DOCUMENT_ROOT'].
                            '/chapter7/admin/error.html.php';
            exit();
    }       

    foreach ($result as $row){
            $authors[] = array('id' => $row['id'], 'name' => $row['name']);
        }

    include 'authors.html.php';

    if (isset($_POST['action']) and $_POST['action'] == 'Delete') {
            include $_SERVER['DOCUMENT_ROOT'].
                            '/chapter7/includes/db.inc.php';
            //Get jokes belonging to author 
            try {
                $sql = 'SELECT id FROM joke WHERE authorid = :id';
                $s = $pdo->prepare($sql);
                $s->bindValue(':id', $_POST['id']);
                $s->execute();
            } catch (PDOException $e) {
                $error ='Error getting list of jokes to delete.';
                include $_SERVER['DOCUMENT_ROOT'].
                                '/chapter7/admin/error.html.php';
                exit();
            }
            $result = $s->fetchAll();
            //Delete joke category entries
            try {
                $sql = 'DELETE FROM jokecategory WHERE jokeid =:id';
                $s = $pdo->prepare($sql);
                //For each joke
                foreach ($result as $row) {
                        $jokeId= $row['id'];
                        $s->bindValue(':id', $jokeId);
                        $s->execute();      
                }
            } catch (PDOException $e) {
                $error = 'Error deleting category entries for joke.';
                include $_SERVER['DOCUMENT_ROOT'].
                                '/chapter7/admin/error.html.php';
                exit();
            }
            //Delete jokes belonging to author
            try {
                $sql = 'DELETE FROM joke WHERE authorid = :id';
                $s = $pdo->prepare($sql);
                $s->bindValue(':id', $_POST['id']);
                $s->execute(); 
            } catch (PDOException $e) {
                $error = 'Error deleting jokes for author';
                include $_SERVER['DOCUMENT_ROOT'].
                                '/chapter7/admin/error.html.php';
                exit();
            }
            //Delete the author
            try {
                $sql = 'DELETE FROM author WHERE id =:id';
                $s = $pdo->prepare($sql);
                $s->bindValue(':id', $_POST['id']);
                $s->execute();
            } catch (PDOException $e) {
                $error ='Error deleting author';
                include $_SERVER['DOCUMENT_ROOT'].
                          '/chapter7/admin/error.html.php';
                exit();
            }
            header('Location: .');
            exit();
    }       

请注意，我对此非常陌生，并且已经尝试过一些惨败的迭代，因此任何帮助，甚至只是简单的指导，可以引导我思考创建此类功能，我将不胜感激。不仅仅是寻找正确的答案，而是想了解背后的想法，如果有人可以提供帮助，那就太好了。

Answer 1

类似的东西应该可以工作。我过去用过这个，它对我很有用。您将需要调整查询等以适应您的数据库和表，但这应该没问题。

$stm = $PdoObj->prepare("SELECT * FROM NEWS_articles");
    $stm ->execute();
    $results = $stm ->fetchAll();

    if($results==null){
        echo "<p>No dice, try other criteria</p>";
    }else{
        foreach($results as $row){
            echo $row["articleName"];
        }
    }