Select distinct values in combobox

I am using asp.net connector and I am trying to load the Dhtmlxcombo with values from database table. But its loading all values. Its not loading the distinct values alone. I given select distinct values only…but its not loading distinct values…
this is how given in ashx file.

[code]dhtmlxComboConnector connector = new dhtmlxComboConnector(

"SELECT DISTINCT PrintableName FROM Country ",
“LeanEngagementNo”,
dhtmlxDatabaseAdapterType.SqlServer2005,
ConfigurationManager.ConnectionStrings[“SamplesDatabase”].ConnectionString,
“PrintableName”
)[/code]