How can we avoid repeating an id

helo

pleas help me.

i have some question about this code.

we have a program that it Make 4 Column and 10 row.(From the database as a random)

Field id from table ads Including 1 to 99 (no repeat)

but some of the data Entered repeated.

How can we avoid repeating it.

For example,

11-32-45-28
56-12-11-99
80-13-20-21
...

Number 11 is repeated

note:there isn't any repeated data in the Database( there is one id=11 in the Database)

i will be glad if you answer to me.

tanks.

<?php
  include("config.php");

  mysql_connect($db_server, $db_username, $db_password);
  mysql_select_db($db_name);

  $query = "SELECT COUNT(ID) FROM ads ";
  $result = mysql_query($query);
  $row = mysql_fetch_array($result);
  $adcnt = $row[0];

  $query = "SELECT * FROM ads ";
  $result = mysql_query($query);
  $i = 1;
  while (($row = mysql_fetch_array($result)))
    {
    $rows[$i] = $row;
    $i++;
    }

  $ids_arr     = null;

    for ($i=1; $i<=10; $i++)
    {
    $ids      = null;

    for ($j=1; $j<=4; $j++)
      {
      $cellno = ($i-1)*4+$j;

        srand((double)microtime()*1000000);
        $adno = mt_rand(1, ($adcnt));
        $ids[$j]     = $rows[$adno]['ID'];
        }

      $ids_arr[$i]     = $ids;
    }
    print( $ids_arr[1][1]);
    print("-");
    print( $ids_arr[1][2]);
    print("-");
    print( $ids_arr[1][3]);
    print("-");
    print( $ids_arr[1][4]);
    echo("<br>");
    print( $ids_arr[2][1]);
    print("-");
    print( $ids_arr[2][2]);
    print("-");
    print( $ids_arr[2][3]);
    print("-");
    print( $ids_arr[2][4]);
    echo("<br>");
    print( $ids_arr[3][1]);
    print("-");
    print( $ids_arr[3][2]);
    print("-");
    print( $ids_arr[3][3]);
    print("-");
    print( $ids_arr[3][4]);
    echo("<br>");
    print( $ids_arr[4][1]);
    print("-");
    print( $ids_arr[4][2]);
    print("-");
    print( $ids_arr[4][3]);
    print("-");
    print( $ids_arr[4][4]);
    echo("<br>");
    print( $ids_arr[5][1]);
    print("-");
    print( $ids_arr[5][2]);
    print("-");
    print( $ids_arr[5][3]);
    print("-");
    print( $ids_arr[5][4]);
    echo("<br>");
    print( $ids_arr[6][1]);
    print("-");
    print( $ids_arr[6][2]);
    print("-");
    print( $ids_arr[6][3]);
    print("-");
    print( $ids_arr[6][4]);


?>

PHP:

 

is the id column set in primary? or unique?

 

i am beginner in php ,but i have one id column in ads table