sql - Select distinct from single column in lightswitch -

i'm trying execute sql query inside lightswitch:

select distinct [columnname] [table] 

the query window has filter, sort, , parameters

i have arrived on dataservice.cs file can manualy edit queries, im stuck here:

    partial void queryname_preprocessquery(ref iqueryable<serviceuser> query)     {         query = query.distinct();     } 

this selects whole table. want distinct values of 1 column. note can add view database , update entity thats not i'm looking for..