count() (aggregation function)
Counts the number of records per summarization group, or total if summarization is done without grouping.
Use the countif aggregation function to count only records for which a predicate returns
This function is used in conjunction with the summarize operator.
Returns a count of the records per summarization group (or in total, if summarization is done without grouping).
This example returns a count of events in states starting with letter
StormEvents | where State startswith "W" | summarize Count=count() by State