adding data in combobox from database

Question

hii frnd ..

i have one combobox in which i'm loading data( text) from database after button click.

it's working properly I'm using Ilist for loading data in combobox... foreach loop for loading all rows.

but after second click of button duplicate data entries showing in the combobox. if i click in third time so

that 3rd time duplicate entries showing in the combobox.

so help me to how to avoid dublicate entery.