数据库内容未显示，分类事件展示PHP代码故障排查求助

Let's walk through the common issues in your code and fix them step by step:

Key Problems in Your Current Code #

1. Empty While Loop: Your while($row2= mysqli_fetch_array($result)) { } doesn't include any code to actually display the data from $row2—it just cycles through the result set without outputting anything.
2. Unfiltered Query: If $result is a generic query without a WHERE clause for the selected category, you're either getting all events (not just the chosen category) or exhausting the result set before your loop runs.
3. Lack of Error Handling: You don't check if your query executes successfully, making it hard to debug if something goes wrong with the database call.

Corrected Code Example #

Here's a revised version that addresses these issues, with security and readability improvements:

<?php
// Assume you have an existing mysqli connection stored in $conn

// Get the selected category from the POST request
$selectedCategory = isset($_POST['category']) ? $_POST['category'] : '';
$result = null;

if (!empty($selectedCategory)) {
    // Use a prepared statement to fetch filtered events (prevents SQL injection)
    $stmt = $conn->prepare("SELECT * FROM events WHERE category = ?");
    $stmt->bind_param("s", $selectedCategory);
    $stmt->execute();
    $result = $stmt->get_result();

    // Check for query errors
    if (!$result) {
        echo "Error loading events: " . $conn->error;
    }
} else {
    // Your working else branch: show all events or default content
    $result = mysqli_query($conn, "SELECT * FROM events");
}

// Display the results
if ($result && mysqli_num_rows($result) > 0) {
    while ($row2 = mysqli_fetch_array($result)) {
        // Replace these with your actual database column names
        echo "<div class='event-card'>";
        echo "<h3>" . htmlspecialchars($row2['event_name']) . "</h3>";
        echo "<p>" . htmlspecialchars($row2['event_description']) . "</p>";
        echo "<span class='category-tag'>" . htmlspecialchars($row2['category']) . "</span>";
        echo "</div>";
    }
} else {
    echo "<p>No events found in this category.</p>";
}
?>

Critical Fixes Explained #

• Added Output Logic: The while loop now renders HTML for each event using data from $row2 (adjust the column names to match your database schema).
• Filtered Prepared Statement: We run a targeted query for the selected category, and use prepared statements to avoid SQL injection vulnerabilities.
• Centralized Result Display: Instead of repeating loop logic for each category, we handle display once after fetching the correct result set.
• Error Checking: We added a check to catch and display database query errors, which helps with debugging.

Quick Form Check #

Make sure your category buttons use the correct name attribute so the POST data is captured properly:

<form method="POST" action="">
    <button type="submit" name="category" value="Healthcare">Healthcare</button>
    <button type="submit" name="category" value="Education">Education</button>
    <button type="submit" name="category" value="Technology">Technology</button>
</form>

内容的提问来源于stack exchange，提问作者umang yadav