Setting mysql row to zero when session user clicks a href / Mysql PHP notification system

Bitwise?

This is a somewhat hard subject. But if you ever used a FLAG in PHP then you used a bitwise number. eg. error_reporting(E_ALL)

Basically what they do is compare the binary value of the number. Which probably makes no sense to you. So I will give you an example. Currently you have 4 boolean values, they are 0 or 1 and require several fields etc. So with a bitwise value you would have this:

notification1 = 1
notification2 = 2
notification3 = 4
notification4 = 8
// notification5 = 16

Now as you can see the value doubles for each one. The reason for this can be explained with some simple math (without getting into the whole 0000001, 0000010 thing).

1+2 = 3  //3 is not 4
1+2+4 = 7 //7 is not 8
1+2+4+8 = 15 // 15 is not 16

Right, so each previous set of numbers must not add up to the next number.

The point of all this is that with the PHP bitwise operators, we can use a single field and tell which of the 4 bits is set in it.

So if user has all notifications on 1-4. Their value is 15 or 1|2|4|8. To check if they have notification 1 turned on, you would do this (with a single & ):

if(1 & 15) echo "true";

Outputs

true

Now, if you wanted to set just 2 say notification 1 and 4. You would do this:

$note_1 = 1;
$note_2 = 2;
$note_3 = 4;
$note_4 = 8;

$mysettings = $note_1|$note_4; //=9

Then we could check it like this:

if($mysettings & $note_1 ) //true
if($mysettings & $note_2 ) //false
if($mysettings & $note_3 ) //false
if($mysettings & $note_4 ) //true

Ok, so a few more examples to drive it home:

 if(1 & 1) //true
 if(1 & 2) //false
 if(1 & 4) //false

 if(1 & 7 ) //true  (1+2+4) or 1|2|4
 if(2 & 7 ) //true ...
 if(4 & 7 ) //true ...

So what this does, is that instead of 4 boolean values we have to store, now we have one integer value that we can tell which of the 4 booleans were set.

Therefore, besides doing some basic arithmetic, it would be possible to elimiate having 4 separate columns, 4 separate fields etc. This bubbles up throughout your code reducing the complexity. Also as a bonus, if you want to add a notification at a later time, you won't have to go though and copy a bunch of code and add another field to your database for the users setting. You can simply add the next double in (in this case 16).

Now UI wise, I would use a set of checkboxes each with one of the bit values. So a user would just check which notification they want and then we just add/subtract it in PHP and save that to one field. Or something similar (like a multi select) where they/you don't have to manually add the values in or try to remember that bit 32 was notification #6.

Also, you could set them as global constants using define

 if(!defined('NOTE_1')) define('NOTE_1', 1);
 if(!defined('NOTE_2')) define('NOTE_2', NOTE_1 * 2);  //1 * 2 = 2
 if(!defined('NOTE_3')) define('NOTE_3', NOTE_2 * 2);  //2 * 2 = 4
 if(!defined('NOTE_4')) define('NOTE_4', NOTE_3 * 2);  //4 * 2 = 8

then you can use them anywhere by simply doing this(assuming $mynotes was a thing):

//$mynotes = NOTE_1|NOTE_4; //9

if($mynotes & NOTE_1) //true

It's pretty slick, and I hope I didn't slaughter that definition of bitwise too much for you guys that know all about it. I was trying to keep it simple, and that is how I think of it as I don't think in binary to good.

Questions>?

UPDATE

For your unrelated question, which should be a separate question. But, as it's ridiculously simple I will indulge you this time.

So you have this.

if($Text1 == 100) {
    $TotalA == 1;
}

This part

$TotalA == 1;

Has 2 = which is comparison not assignment. Simply remove one of the =. It's actually perfectly valid in PHP to do comparison outside of an if statement. For example if you did (assuming you dont get an undefined variable error):

 var_dump($TotalA == 1);

It would say something like one of these two

 bool(true)
 bool(false)

You get the error, because doing comparison requires a read from the variable, which hasn't been set, because this was supposed to be doing the setting. But because, as I said, this is comparison -- there is no setting taking place.

UPDATE1

So back to the bitwise stuff... I wanted to show the effect this will have on your code. So taking just a small bit of your code (abbreviated):

$query = mysql_query("SELECT * FROM users WHERE username = '$username'"); 
while($row = mysql_fetch_assoc($query)){ 
    //uses 4 columns, if we need to add a notification we have to add another column and change this code.
    //more concerning is we would need to change the DB schema
    $Notificare1 = $row['Notificare1'];
    $Notificare2 = $row['Notificare2'];
    $Notificare3 = $row['Notificare3'];
    $Notificare4 = $row['Notificare4'];
    ....
    if($Notificare1 == 1) {
        $Notificare1 = "<li><a href='settings.php'>
        <div class='user_img'> ... ";
    }
    if($Notificare2 == 0){
       $Notificare2 = "<li></li>";
    }
    if($Notificare2 == 1) {
       $Notificare2 = "<li><a href='#subdomenii'> ...";
    }
 ...
 }

Doing the same thing with Bitwise (assuming we defined the constants that I outlined above):

$query = mysql_query("SELECT * FROM users WHERE username = '$username'"); 
while($row = mysql_fetch_assoc($query)){ 
    //uses 1 column, if we add another notification then no changes are required here.
    $Notificare = $row['Notificare'];
    ...
    if($Notificare & NOTE_1) {
        $Notificare1 = "<li><a href='settings.php'>
            <div class='user_img'> ... ";
    }
    if($Notificare & NOTE_2){
        $Notificare2 = "<li></li>";
    }else{ //changed the if to an else, if it's not true it must be false.
        $Notificare2 = "<li><a href='#subdomenii'> ...";
    }
    ...
}

SQL Queries. MySql has its own equivalent set of bitwise operators. You can view the documentation for those here. These work pretty much the same what as they do in PHP. So you can do this:

$sql = 'SELECT count(id) as count FROM users WHERE Notificare & '.NOTE_1; //constants are one of the few things I would say is safe to concatenate in a query as they are immutable.

So this would give you the number of users that have Notification #1 set.

PARTING NOTES

I noticed two other pretty big issues, both dealing with your SQL query

 mysql_query("SELECT * FROM users WHERE username = '$username'");

Firstly the mysql_* set of functions are depreciated as of PHPv5.6 (I think) and removed as of PHPv7 (I know for sure). So you will want to use a different database driver. I suggest using PDO instead of MySqli, I haven't used MySqli for about 4 years (in production code), and I haven't missed it. I may be a bit biased on it.

Secondly concatenating variables into SQL leaves you with SQLInjection vulnerabilities. This is were an attacker inserts some SQL of their own into the query. An example would be where $username = "'; DROP TABLE users; --". So putting it into your SQL we get something like this (please don't run it)

 SELECT * FROM users WHERE username = ''; DROP TABLE users; --' // using -- is the start of a line comment in SQL, so anything after that is ignored..

Which would run the first query and then Drop(delete) the table. This is a bad example because there are some settings that prevent running multiple queries, but they are not always configured correctly.

To prevent this, both PDO, and MySqli have Prepared Statements. You could also argue that the data comes from $_SESSION so it must be clean, but where did it get put in there from? It's hard to tell. So Prepared Statements are designed to be used near the Point Of Failure, or where the query is executed. So we can clearly see that the query is safe without having to dig through files and files to check where that data came from.

But as this post is long enough I will leave that discussion for another time. I would feel remiss if I didn't point those 2 issues out.