title: divide the comma separated string into columns with empty string
body: <p>I have a following string like this</p>
  
  <pre><code>str:=',1,,3,4,5,6,,8,9';
  str2:=',a,l,,gj,,b';
  </code></pre>
  
  <p>How can I divide the comma and separated string into columns like this with using SQL only? (the ordering should be same as below)</p>
  
  <pre><code>COL
  ---------
  NULL
  1
  NULL
  3
  4
  5
  6
  NULL
  8
  9
  
  COL2
  ----------
  NULL
  a
  l
  NULL
  gj
  NULL
  b
  </code></pre>
  
  <p>Thanks </p>