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# countdistinct()

`countdistinct(col [, ...cols])` counts the number of distinct values of the provided column(s) in the input stream. If multiple columns are provided, their values are treated as a tuple.

## Technical Notes

* If there are at most 1000 distinct values in the input stream, it will return the exact value.
* If there are >1000 distinct values, it will fall back to a variant of the [hyperloglog algorithm](https://en.wikipedia.org/wiki/HyperLogLog) with a precision of 14.
  * For most inputs, this has an average error of 0.5% and a p95 error of 1.5%.

## Returns

A table with one row and one column, called `@q.uniq`.

## Example

Analyze AWS CloudTrail logs to count the number of distinct IAM users making AWS API calls.

```python
@scnr.source_type: "aws:cloudtrail"
and userIdentity.type: "IAMUser"
| countdistinct(userIdentity.arn)
```


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