Merge pull request #222259 from eternovsky/main

Call out TimeGenerated requirement in xform kql

Author: prmerger-automator[bot]

articles/azure-monitor/essentials/data-collection-transformations-structure.md

@@ -39,6 +39,8 @@ Transformations in a [data collection rule (DCR)](data-collection-rule-overview.
 
 
 
+### Required columns
+The output of every transformation must contain a valid timestamp in a column called `TimeGenerated` of type `datetime`. Make sure to include it in the final `extend` or `project` block! Creating or updating a DCR without `TimeGenerated` in the output of a transformation will lead to an error.
 
 ## Inline reference table
 The [datatable](/azure/data-explorer/kusto/query/datatableoperator?pivots=azuremonitor) operator isn't supported in the subset of KQL available to use in transformations. This operator would normally be used in KQL to define an inline query-time table. Use dynamic literals instead to work around this limitation.
@@ -329,4 +331,4 @@ Use [Identifier quoting](/azure/data-explorer/kusto/query/schema-entities/entity
 
 ## Next steps
 
-- [Create a data collection rule](../agents/data-collection-rule-azure-monitor-agent.md) and an association to it from a virtual machine using the Azure Monitor agent.
+- [Create a data collection rule](../agents/data-collection-rule-azure-monitor-agent.md) and an association to it from a virtual machine using the Azure Monitor agent.