Description:
------------
There is currently a function to do absolute seek in Mysql API.

When you need to to relative seek , you have to implement integer counter to keep track of the current cursor position. Then call seek

here is a sample code:
   //iterating over rows
   for/while....{
       mysql_fetch_xxxx(....);
       $current_row++;

       [...]
       // call relative seek
       $current_row+= $seek_offset;
       mysql_data_seek($id, $current_row);


This quite simple but when the code gets complicated, it s easy to miss on $current_row update. The only only solution is to encapsulate php mysql function in additional abstraction layer to handle counter updates safely.

I suppose the internal counter is already available in mysql module. 
What I am suggesting, is to expose this internal counter by adding a new function to mysql API.