Q:

MYSQL/PHP - Random row with %

I'm trying to make a random encounter with a monster based on %. 
I got in my MySQL database a column called "monster_chancespawn" :

Monster 1 got 50%
Monster 2 got 30%
Monster 3 got 20%

What I want to do is to do a random MySQL SELECT in my "monster" DATABASE based on these %. 
I already got this
    $monsterspawn=$db->prepare('SELECT * FROM monster');
    $monsterspawn->execute();
    $monsterspawn->CloseCursor();

    foreach ($monsterspawn as $infospawn)
      { 
      echo .  $infospawn["monster_chanceloot"] . ; 
      }

With this, it normally echo "50 30 20", but nothing really useful. 
What I want to do is :

Getting each monster's chances of loot. 
Maybe doing something like "If rand is between 0 and 50, spawn Monster 1.  If it is between 50 and 80, spawn Monster 3.  If it is between 80 and 100, spawn Monster 3.  BUT I want this to be flexible, and to change when I change the monster_chanceloot value

I could do something like this I guess
$randomspawn = rand(0, 100);
if ($randomspawn >= 0 && $randomspawn <= $infospawn["monster_chanceloot"])
{ $monstername = "Monster1" }

   elseif ($randomspawn >= $infospawn["monster_chanceloot"] && $randomspawn <= $infospawn["monster_chanceloot"](Monster 2's one))
    { $monstername = "Monster2" }

And same thing for Monster 3.  The main problem would be that is does not let me change the number of monsters available, and the other problem is that I don't know how to get the monster_chanceloot of each monster outside of the foreach.  And I don't want to make 30 MYSQL connection, so avoid using it each time. 
Thanks ! 
EDIT : Here is a possibility given by "German Drulyk" :
I got Monster1, Monster2, Monster3. 
I duplicate Monster1 2times in my database and Monster2 1time. 
I have now 3 Monster1, 2 Monster2 and 1 Monster3. 
So : 50% of chance to pick a Monster1, 33,3 for Monster 2 and 16,6 for Monster 3. 
To get more accurate results, you can copy them to 100 to have 1 monster = 1%.  To get a monster, simply do :
    $query=$db->prepare('SELECT * FROM MONSTERDDB ORDER BY RAND() LIMIT 1');
    $query->execute();

A:

IF you will never exceed 100 monsters in a zone then you need a table with 3 columns; zone_id, chance, monster_id
Per zone, insert 100 records and set the chance to 1 through 100 inclusively. 
Per record, add a monster_id respective to it's common-ness; all 100 records per zone should have a monster_id
For example, zone1 needs 50 records with monster1, 30 records for monster2, and 20 records for monster3
In PHP, you can write your query like so
$sql = "select
          monster_id
        from
          table_name
        where
          zone_id = $zoneId and
          chance = ".rand(1, 100);

Additionally, I have not tried this but I guess native MySQL can achieve the same effect:
$sql = "select
          monster_id
        from
          table_name
        where
          zone_id = $zoneId and
          chance = FLOOR( 1 + RAND() * 100 )";

