Dear,

As far as i know, there is no no-code way to achieve this.

but i might think of 2 options.

first is to restrict users somehow from entering duplicate values into the list itself... i am not really sure if users entering their data from the sharepoint list itself or a custom web part... either way you might wanna find a way to restrict them from entering duplicates.... to have no duplicate when you retrieve the data.

second way is to create a custom service broker and use it as data source... and inside that custom service broker your code will retrieve only distinct values.

Hope it helps..

Regards..