Hi,
I published map service on ArcGIS Server 10.3.1, I see in Advanced Query Capabilities section "Supports Distinct : false" in rest directory, When I try to query using Query with query.returnDistinctValues = true; parameter, It doesn't return unique values from the layer.

I don't see option in capabilities while you publish map service on ArcGIS Server.
How to enable "Supports Distinct : true" ?
Am I missing anything ?
Thanks,
Mayur