Why Does `mysqli_stmt::bind_result()` Throw an Error When the Number of Bind Variables Doesn't Match the Result Set Columns?

Binding Variable Mismatch in mysqli_stmt::bind_result()

In PHP, when executing a prepared statement using mysqli_stmt::bind_result(), the number of bind variables must correspond to the number of fields in the result set. If they don't match, the error "mysqli_stmt::bind_result(): Number of bind variables doesn't match number of fields in prepared statement" is thrown.

To resolve this issue, ensure that the number of bind variables in bind_result() aligns with the number of columns returned by the query. Consider the following PHP code:

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

In this example, the prepared statement retrieves two columns, username and password. However, only one bind variable, $username, is specified in bind_result(). To correct this, add the second bind variable for $password:

$stmt->bind_result($username, $password); // Correct number of bind variables

The syntax for SELECT statements is: SELECT field1, field2, ... fieldN FROM table_name WHERE .... Each field must be separated by a comma, not an AND condition.

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