count_distinctif() (aggregation function) - (preview)

Applies to: ✅ Microsoft Fabric ✅ Azure Data Explorer ✅ Azure Monitor ✅ Microsoft Sentinel

Conditionally counts unique values specified by the scalar expression per summary group, or the total number of unique values if the summary group is omitted. Only records for which predicate evaluates to true are counted.

Note

This function is used in conjunction with the summarize operator.

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

Note

• This function is limited to 100M unique values. An attempt to apply the function on an expression returning too many values will produce a runtime error (HRESULT: 0x80DA0012).

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

Syntax

count_distinctif (expr, predicate)

Learn more about syntax conventions.

Parameters

Name	Type	Required	Description
expr	scalar	✔️	The expression whose unique values are to be counted.
predicate	string	✔️	The expression used to filter records to be aggregated.

Returns

Integer value indicating the number of unique values of expr per summary group, for all records for which the predicate evaluates to true.

Example

This example shows how many types of death-causing storm events happened in each state. Only storm events with a nonzero count of deaths will be counted.

Run the query ::: moniker-end

StormEvents
| summarize UniqueFatalEvents=count_distinctif(EventType,(DeathsDirect + DeathsIndirect)>0) by State
| where UniqueFatalEvents > 0
| top 5 by UniqueFatalEvents

Output

State	UniqueFatalEvents
TEXAS	12
CALIFORNIA	12
OKLAHOMA	10
NEW YORK	9
KANSAS	9