php - MySQLi prepared statement fails where identical regular query succeeds

I have a conventional query that works just fine that looks like this:

$result = $mysqli->query("SELECT value FROM activities WHERE name = 'Drywall'");

This succeeds in returning a row. However, for the purposes of diagnosing the problem I'm having with a prepared statement, I tried an identical query as a prepared statement like so:

$stmt = $mysqli->prepare("SELECT value FROM activities WHERE name = 'Drywall'");
$stmt->execute();

Despite the fact these are identical query strings, $stmt->num_rows is always 0. Why would the conventional query work, but the prepared statement not when they are the same exact query? Also, I realize including 'Drywall' in the prepared query string runs counter to the purpose of prepared statements, but I was just trying to eliminate the possibility that bind_param() was the culprit. So I was using bind_param() to fill in placeholders and that wasn't working either, despite my double-checking at runtime that the variable I was binding contained the correct value.

Answer

I think you want to use

$stmt->store_result();

before the call

$stmt->num_rows();

see last line of the descripton in the manual for $stmt->num_rows() (http://www.php.net/manual/en/mysqli-stmt.num-rows.php).