count_distinct() (aggregation function) - (preview)

Counts unique values specified by the scalar expression per summary group, or the total number of unique values if the summary group is omitted.

If you only need an estimation of unique values count, we recommend using the less resource-consuming dcount aggregation function.

To count only records for which a predicate returns true, use the count_distinctif aggregation function.

Syntax

count_distinct (expr)

Parameters

Returns

Long integer value indicating the number of unique values of expr per summary group.

Example

The following example shows how many types of storm events happened in each state.

Function performance can be degraded when operating on multiple data sources from different clusters.

StormEvents
| summarize UniqueEvents=count_distinct(EventType) by State
| top 5 by UniqueEvents

Output

Related content

• Aggregation function types at a glance
• count_distinctif() (aggregation function)
• count() (aggregation function)
• countof()
• countif() (aggregation function)