SQL数据库存储/检索图片失败，代码触发mysql函数参数异常警告

Why You're Seeing Those Warnings #

The two warnings stem from mixing deprecated mysql_* functions with modern mysqli_* functions—they’re not compatible! Here’s the breakdown:

• mysql_select_db() expects its first parameter to be a database name (string), but you passed a mysqli connection object (from mysqli_connect()).
• mysql_query() expects an SQL string as its first parameter, but you likely passed the connection object instead (again, mixing function families).

On top of that, mysql_* functions are no longer supported in PHP 7+, so we’ll switch entirely to mysqli_* for a secure, working solution.

Step-by-Step Fixes #

1. Correct Database Connection #

Replace your existing connection code with this consistent mysqli version (it eliminates the need for a separate select_db call):

// Database credentials
$host = "localhost";
$username = "your_db_user";
$password = "your_db_pass";
$dbname = "your_db_name";

// Create connection and select database in one step
$conn = mysqli_connect($host, $username, $password, $dbname);

// Check for connection errors
if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
}

2. Fix Image Upload Logic #

First, ensure your database table has a column of type BLOB (or MEDIUMBLOB for larger images) to store the image data. Then update your form and processing code:

<!DOCTYPE html>
<html>
<body background="bla.jpg">
<h3>Register with us</h3>
<form enctype="multipart/form-data" method="POST">
    <input type="file" name="image" />
    <input type="submit" name="submit" value="Upload Image" />
</form>
</body>
</html>

<?php
if (isset($_POST['submit']) && isset($_FILES['image'])) {
    // Check if upload was successful
    if ($_FILES['image']['error'] !== UPLOAD_ERR_OK) {
        die("Upload failed with error code: " . $_FILES['image']['error']);
    }

    // Sanitize image data to prevent SQL injection
    $imageName = mysqli_real_escape_string($conn, $_FILES['image']['name']);
    $imageData = mysqli_real_escape_string($conn, file_get_contents($_FILES['image']['tmp_name']));

    // Insert image into database
    $sql = "INSERT INTO your_table_name (image_name, image_data) VALUES ('$imageName', '$imageData')";
    if (mysqli_query($conn, $sql)) {
        echo "Image uploaded successfully!";
    } else {
        echo "Error: " . $sql . "<br>" . mysqli_error($conn);
    }
}

// Close connection when done
mysqli_close($conn);
?>

3. Key Improvements & Checks #

• Replace your_db_user, your_db_pass, your_db_name, and your_table_name with your actual database details.
• Add file type validation to block malicious uploads (optional but recommended):

  $allowedTypes = ['image/jpeg', 'image/png'];
  if (!in_array($_FILES['image']['type'], $allowedTypes)) {
      die("Only JPG and PNG files are allowed.");
  }
  

• Use MEDIUMBLOB instead of BLOB if you’re uploading images larger than 64KB.

Retrieving Stored Images #

To display an image later, create a separate file (e.g., get_image.php) to fetch and output the data:

<?php
$conn = mysqli_connect("localhost", "your_db_user", "your_db_pass", "your_db_name");
$imageId = $_GET['id']; // Use your table's unique ID column

$sql = "SELECT image_data, image_name FROM your_table_name WHERE id = $imageId";
$result = mysqli_query($conn, $sql);
$row = mysqli_fetch_assoc($result);

// Set correct MIME type based on file extension
$extension = pathinfo($row['image_name'], PATHINFO_EXTENSION);
$mime = ($extension === 'png') ? 'image/png' : 'image/jpeg';

header("Content-Type: $mime");
echo $row['image_data'];
mysqli_close($conn);
?>

Display it in your HTML like this: <img src="get_image.php?id=1" alt="Uploaded Image">

内容的提问来源于stack exchange，提问作者happyswine44