MySQL warning

I am getting the following warning when updating user information or when a new user creates an account:

user warning: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '' at line 1 query: SELECT * FROM users_roles WHERE uid = 2 AND rid = in /home/bedigiti/public_html/_theparadox/includes/database.mysql.inc on line 172.

The relevant code appears to be:

/**
 * Supporting functions
 */

function _role_control_grant_role($user, $roleid) {
	// Verify this user isn't in this role already
	$result = db_query("SELECT * FROM {users_roles} WHERE uid = $user->uid AND rid = $roleid");
	$role_already_given = db_num_rows($result);
	if (!$role_already_given) {
		db_query('INSERT INTO {users_roles} (uid, rid) VALUES (%d, %d)', $user->uid, $roleid);
	}
}

function _role_control_deny_role($user, $roleid) {
	// Verify membership
	$result = db_query("SELECT * FROM {users_roles} WHERE uid = $user->uid AND rid = $roleid");
	$role_present = db_num_rows($result);
	if ($role_present) {
		db_query("DELETE FROM {users_roles} WHERE uid = %d AND rid = %d", $user->uid, $roleid);
	}
}