Display a message in KQL when no results or conditions match

Question

How can I display a message if there are no results for the condition below, allowing it to be pinned to a dashboard ?

Perf
| where (CounterName == "% Processor Time")
| where _SubscriptionId contains "**************"
| summarize CPU_Used=avg(CounterValue) by bin(TimeGenerated, 24h), Computer =  tostring(split(Computer, ".")[0])
| where CPU_Used > 85 and CPU_Used < 95
| render timechart

Trying below query encounter with error

Answer 1

@$@chin thank you for the question and providing additional details.

The iff() function cannot be used in this case as the "then" and "else" parameters requires a scalar datatype (or inbuilt data type like numbers, string etc.), The provided type is not evaluated which means "render timechart" will not work.

For your requirement, you could simply use the query. If there are no data available to plot anything, by default, the pinned visual on Azure dashboard will show "No data for the given query" (which cannot be customized at the moment):

Hope this helps.

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Answer 2

Hello, the error you have is a syntax one, iif() would be something like this eample, using extend.
However this wont solve your main issue, as the line "| where CPU_Used > 85 and CPU_Used < 95" means the next line isnt evaluated, as only the results between 85 --> 95 are shown. Remember that KQL is filtering the input, and you've filtered the answer out, just leaving null at this stage. By default you get "No results found from the last 24 hours" message. Azure Workbooks allow you to supply an alternative message, but I dont know if Azure Dashboards do that?

| extend noresults_ = iif(isempty(CPU_Used),"y","n")