This tabular form makes the column Col3 read only when it contains a value - as described here: https://forums.oracle.com/forums/thread.jspa?messageID=10184388

1. Give the tabular form a static ID. I called this one: readonly-tabular
2. Figure out the name attribute of the column you wish to make read only. In this cae, it is f04.
3. Create a new dynamic action:
   Event: Page Load
   
4. True Action: Execute JavaScript code
   Code:

   
   var els = $('#readonly-tabular input[name="f04"]');
   els = els.filter(function(index){
     return $(this).val() != "";
   });
   
   els.attr("readonly", true);
   
   

5. In the true action, ensure you select the option: Fire On Page Load