While loop inside while loop

Hi, I am new to PHP. Can anyone tell me how to use while loop inside while loop?

 

example

PHP:

<?php
$i=1;
while($i<5)
      {
          $j=1
           while($j<$i)
           {
            echo $j." ";
             $j++;
            }
      echo "<br>";
      }


out put would be
1 2 3 4 5
1 2 3 4
1 2 3
1 2
1