What is the significance of the error message "Warning: mysqli_error(): Couldn't fetch mysqli" in the context of PHP form submission?

The error message "Warning: mysqli_error(): Couldn't fetch mysqli" indicates that there is an issue with the connection to the MySQL database when using the mysqli extension in PHP. This error commonly occurs when there is a problem with establishing a connection to the database or when the connection is lost during the execution of a query. To solve this issue, you should check the database connection parameters, ensure that the connection is established before executing queries, and handle any potential errors that may occur during database operations.

// Establish database connection
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "database";

$conn = mysqli_connect($servername, $username, $password, $dbname);

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

// Perform database operations
$sql = "SELECT * FROM table";
$result = mysqli_query($conn, $sql);

if (!$result) {
    die("Error: " . mysqli_error($conn));
}

// Close connection
mysqli_close($conn);