Why Does `mysqli_stmt::bind_result()` Throw a 'Binding Mismatch' Error in PHP Login Forms?

Mysqli_stmt::bind_result() Error: Binding Mismatch

When attempting to implement a PHP login form using a prepared statement, users may encounter the following error:

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

This error indicates a discrepancy between the number of variables specified in bind_result() and the number of fields returned by the prepared statement. To resolve this issue, examine the following code snippet:

$mysqli = new mysqli("localhost", "root", "", "security");

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

Root Cause:

The incorrect syntax in the SELECT statement is the root cause of the error. The correct syntax should be:

SELECT username, password FROM users WHERE username = ?

Resolution:

The issue can be resolved by separating the fields in the SELECT statement with a comma instead of "AND." The correct code is provided below:

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

By ensuring the correct syntax in the SELECT statement and observing the number of bind variables matches the number of fields in the prepared statement, the mysqli_stmt::bind_result() error can be prevented.

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