# DISTINCTCOUNTHLL

Returns an approximate distinct count using *HyperLogLog*. It also takes an optional second argument to configure the *log2m* for the *HyperLogLog*. 

For accurate distinct counting, see [DISTINCTCOUNT](https://docs.pinot.apache.org/release-1.3.0/configuration-reference/functions/distinctcount). Review [DISTINCTCOUNTHLL considerations](#distinctcounthll-considerations) for your use case.

## Signature

> DISTINCTCOUNTHLL(colName, log2m)

## Usage Examples

These examples are based on the [Batch Quick Start](https://docs.pinot.apache.org/release-1.3.0/basics/getting-started/quick-start#batch).

```sql
select DISTINCTCOUNTHLL(teamID) AS value
from baseballStats 
```

| value |
| ----- |
| 158   |

```sql
select DISTINCTCOUNTHLL(teamID, 12) AS value
from baseballStats 
```

| value |
| ----- |
| 149   |

## **DISTINCTCOUNTHLL considerations**

* `DISTINCTCOUNTHLL()`is faster than `DISTINCTCOUNT()`if data is pre-aggregated at ingestion or aggregated at a server with enough records. This performance improvement increases when comparing large datasets.
* If very few records are pre-aggregated, `DISTINCTCOUNTHLL()`will not be as fast as `DISTINCTCOUNT()`because the serialized HLL size is larger than sending individual values.
* `DISTINCTCOUNTHLLPLUS()`provides more precise results than `DISTINCTCOUNTHLL()`with the same performance.
* `DISTINCTCOUNTSMARTHLL()`automatically shifts to HLL when reaching a threshold, and comes with some overhead.


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.pinot.apache.org/release-1.3.0/configuration-reference/functions/distinctcounthll.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.