It,s very simple you need to append all that values to a single column in sql query and bind that column to value field of dropdownlist.Then by the help of split fuction you can get all the value...
Example-
select name + '-' + branch + '-' + rollno as value from yourtablename
here you can bind the value column to the dropdownlist value field.
on the C# page use code as as below
var value= ddl.SelectedValue.Split('-').ToList();
String name=lowerUpperval[0];
String branch= lowerUpperval[1];
String rollno=lowerUpperval[2];
Enjoy
Happy Codding!!!