What are the best practices for avoiding duplicate database entries when submitting form data multiple times?

To avoid duplicate database entries when submitting form data multiple times, you can implement a check in your PHP code to see if the data already exists in the database before inserting it. One way to do this is by checking for a unique identifier or key in the form data and querying the database to see if a record with that key already exists. If it does, you can update the existing record instead of inserting a new one. 

// Check if the form has been submitted
if ($_SERVER["REQUEST_METHOD"] == "POST") {
    
    // Check if the data already exists in the database
    $key = $_POST['unique_key']; // Change 'unique_key' to the actual unique identifier in your form data
    $query = "SELECT * FROM your_table WHERE unique_key = '$key'";
    $result = mysqli_query($connection, $query);

    if (mysqli_num_rows($result) > 0) {
        // Update existing record
        $update_query = "UPDATE your_table SET column1 = 'new_value' WHERE unique_key = '$key'";
        mysqli_query($connection, $update_query);
    } else {
        // Insert new record
        $insert_query = "INSERT INTO your_table (unique_key, column1) VALUES ('$key', 'value')";
        mysqli_query($connection, $insert_query);
    }
}

Keywords

PHP database unique constraint INSERT IGNORE ON DUPLICATE KEY UPDATE

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