$stmt2 = $db->prepare("INSERT INTO friend(`uId`,`friendId`) VALUES (?,?), VALUES(?,?)");
$stmt2->bind_param('ssss', $userId,$friendId,$friendId,$userId);
I expect it would insert 2 rows with the result
uId friendId
1 2
2 1
but it returned
Call to a member function bind_param() on a non-object