# APPROX\_COUNT\_DISTINCT\_ESTIMATE

Returns an estimate of the number of distinct values for one or more [HyperLogLog](http://en.wikipedia.org/wiki/HyperLogLog) states.

## Syntax

```sql
APPROX_COUNT_DISTINCT_ESTIMATE ( expr )

```

## Arguments

**expr**

An expression evaluating to a scalar value of type `VARBINARY(16384)`. This scalar value is the HyperLogLog state for which `APPROX_COUNT_DISTINCT_ESTIMATE` returns the number of distinct values.

`expr` may be the name of a column. In this case, `APPROX_COUNT_DISTINCT_ESTIMATE` combines values in the column (which are HyperLogLog states) and returns the number of distinct values in the combined state.

## Remarks

This function is used in conjunction with `APPROX_COUNT_DISTINCT_ACCUMULATE` and `APPROX_COUNT_DISTINCT_COMBINE`. To best understand its usage, see the topic [Distinct Count Estimation Functions](https://docs.singlestore.com/db/v9.1/reference/sql-reference/distinct-count-estimation-functions.md).

***

Modified at: February 24, 2023

Source: [/db/v9.1/reference/sql-reference/distinct-count-estimation-functions/approx-count-distinct-estimate/](https://docs.singlestore.com/db/v9.1/reference/sql-reference/distinct-count-estimation-functions/approx-count-distinct-estimate/)

(An index of the documentation is available at /llms.txt)