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# CountDistinct

> Use the Sigma CountDistinct function to return the number of unique values within a column or group.

The **CountDistinct** function returns the number of unique values within a column or group.

The **CountDistinct** function is an aggregate function.

Aggregate functions evaluate one or more rows of data and return a single value.

In a table element, the aggregate is calculated for each grouping. For information on how to add a grouping with an aggregate calculation to a table, see [Group columns in a table](/docs/create-and-manage-tables#group-columns-in-a-table).

In a table with no groupings, the aggregate is calculated for each row. For information on how to calculate summary statistics across all rows in a table, see [Add summary statistics to a table](/docs/create-and-manage-tables#add-summary-statistics-to-a-table).

To learn more about using aggregate functions, see [Building complex formulas with grouped data](https://www.sigmacomputing.com/resources/training-videos/table-grouping-and-functions#complex-formulas).

## Syntax

`CountDistinct(column)`

Function arguments:

* **column** (required) The column of values to be counted. Duplicate and Null or empty values are not counted.

## Example

`CountDistinct([City])`

* Returns the number of unique city names.

## Related resources

* [Count](/docs/count)
* [CountIf](/docs/countif)