Azure Log Analytics - Unable to use ItemCount in union result

Question

I'm trying to write a Kusto query that will union myUnion with AppTraces logs. All works until I declare ItemCount column as part of myUnion results. You can do this with other columns, e.g. TimeGenerated.

The error returned is

'project' operator: Failed to resolve scalar expression named 'ItemCount'

let countRequests = 5;
let myUnion =  union  (print
            TimeGenerated = now(),
            Message = "MyMessage",
            ItemCount = countRequests);
AppTraces
| union myUnion
| project
    TimeGenerated,
    ErrorMessage = Message,
    ItemCount
| order by TimeGenerated asc

Possible workaround: I can name myUnion.ItemCount something else and coalesce, but I'd preferably like to use the built-in ItemName.

Answer 1

you might have a conflicting column named ItemCount with a different datatype in your table named AppTraces.

what does the following return?

let countRequests = 5
;
let myUnion =  print TimeGenerated = now(),
    Message = "MyMessage",
    ItemCount = countRequests
;
AppTraces
| union myUnion
| getschema

if you see two columns with different datatypes, for example ItemCount_int and ItemCount_long - you'll want to align the data types (e.g. by switching to let countRequests = int(5))