Why Does `mysqli_stmt::bind_result()` Throw a Bind Variable Mismatch Error?

Bind Variable Mismatch in PHP's mysqli_stmt::bind_result()

When attempting to log in using a PHP login form with a prepared statement, you encounter the error:

mysqli_stmt::bind_result(): Number of bind variables doesn't match number of fields in prepared statement

Diagnosis:

This error occurs when the number of bind variables specified in bind_param() does not match the number of fields returned by the prepared statement.

Solution:

In your code:

$stmt->prepare("SELECT username AND password FROM users WHERE username = ?");

The prepared statement retrieves two fields, username and password, but your subsequent bind_param() and bind_result() calls specify only one bind variable, $username.

To resolve this, you need to correctly specify multiple bind variables and fields:

$mysqli->prepare("SELECT username, password FROM users WHERE username = ?");
$username = $_POST['name'];
$stmt->bind_param('s', $username);
$stmt->execute();
$stmt->bind_result($username, $password);

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