Issue with KQL / Kusto distinct, extend and project

Question

I don't really understand what's the issue if you want to use the command distinct and distinct count AFTER a project or extend operators.

let planting_table = ['events.all'] 
    | where FullName_Name == "plant_seed" 
    | extend SeedName = EventData.Payload.SeedName,
        OasisName = EventData.Payload.OasisName,
        TileName = EventData.Payload.TileName
    | project-away SchemaVersion, FullName_Namespace, Entity_Id, Entity_Type,
        EntityLineage_title, EventData, EntityLineage_title_player_account,
        EntityLineage_namespace, ExperimentVariants, FullName_Name
    | project-rename id = EntityLineage_master_player_account
;
planting_table
| summarize dcount(SeedName) by id

My goal is to make a distinct count of the seedname by ID in Kusto / KQL. How can I do that? Why I cannot use distinct after a extend or a project operator?

Thanks for the help!

Answer 1

try casting the dynamic property named SeedName to string, using the tostring() function, so that you can aggregate over it using the distinct operator.

i.e.

...
| extend SeedName = tostring(EventData.Payload.SeedName),
...
| summarize dcount(SeedName) by id