OK well here's how you get started:
Make sure you have your db query setup properly, and in working order.
Once you have the query, you'll want to execute it with the function
mysql_query(). Place the results into a variable such as $results.
Now you set up your while loop. Use the function
mysql_fetch_array(). There is a nice example on that page that show just how to formulate the while loop.
Before you can echo each option for the select, you'll going to have to split apart the SIZE field based on your delimiter of choice. This is done inside the while loop, as you have to do it each time. Check out
explode(). You could also use preg_split or split, but in the absence of the need for a regular expression, explode will be the fastest option. Put the results of the explode function into an array.
Next you'll need a new while loop. The first while loop went through each item in you quesry result, this one goes inside that one and loops through each exploded SIZE for the corresponding row.
Finally, put the echo statement in now. As the inner while loop iterates, it will output the correct option for your select. When it finishes the outer loop will iterate and repeat the entire process for the next row in the result.
Post your code as you go if you need help.
peace