How to omit duplicate items in a dynamic dropdownlist in asp.net using c#

i have created a dynamic dropdownlist control to a column of a pre existing table in sql DB.that columns contain repeated values but i want to omit those duplicate values. 

I thought of two ways.. First one is to add the column values to the dropdownlist by omiting the repeated values using looping conditions.But i'm not able to guess the logic.. 

second one is to add all the values of the column to the dropdownlist and then delete the duplicate values...

Plz send  suggestions for any of the above methods....