how to bind from comma separated string to checkbox in gridview using asp.net

I have table called Account like this,

ID   Code   X-Ref
1    1.1    NULL
2    1.2    NULL
3    1.3    NULL
...

I have binded Code values to dropdownlist, when i select code value in dropdown the gridview will display rest of the code values(i.e.,Except the one which i have selected in dropdownlist).

I have a checkbox in gridview when i select some of the row and click ok it will update the table with respect to code ID like as shown below,

ID   Code   X-Ref
1    1.1    1.2,1.3
2    1.2    1.1,1.3,1.4
3    1.3    1.2,1.4
...

Now the question is how to populate from database with checkbox enabled in gridview.. example.., if i select 1.1 in drop down list the checkboxes of both row 1.1 and 1.3 should be checked in gridview. How to do that please help..