uniqCombined64

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## uniqCombined64[​](#uniqCombined64 "Direct link to uniqCombined64")

Introduced in: v20.1.0

Calculates the approximate number of different argument values.
It is the same as [`uniqCombined`](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/uniqcombined), but uses a 64-bit hash for all data types rather than just for the String data type.

This function provides the result deterministically (it does not depend on the query processing order).

Note

Since it uses 64-bit hash for all types, the result does not suffer from very high error for cardinalities significantly larger than `UINT_MAX` like [`uniqCombined`](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/uniqcombined) does, which uses a 32-bit hash for non-String types.

Compared to the [uniq](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/uniq) function, the uniqCombined64 function:

- Consumes several times less memory
- Calculates with several times higher accuracy

Details

Implementation details
This function calculates a 64-bit hash for all data types for all parameters in the aggregate, then uses it in calculations.
It uses a combination of three algorithms: array, hash table, and [HyperLogLog](https://en.wikipedia.org/wiki/HyperLogLog) with an error correction table:

- For a small number of distinct elements, an array is used
- When the set size is larger, a hash table is used
- For a larger number of elements, HyperLogLog is used, which will occupy a fixed amount of memory

**Syntax**

```
uniqCombined64(HLL_precision)(x[, ...])
uniqCombined64(x[, ...])
```

**Parameters**

- `HLL_precision` — Optional. The base-2 logarithm of the number of cells in HyperLogLog. The default value is 17, which is effectively 96 KiB of space (2^17 cells, 6 bits each). Range: [12, 20]. [`UInt8`](/docs/sql-reference/data-types/int-uint)

**Arguments**

- `x` — A variable number of parameters. [`Tuple(T)`](/docs/sql-reference/data-types/tuple) or [`Array(T)`](/docs/sql-reference/data-types/array) or [`Date`](/docs/sql-reference/data-types/date) or [`DateTime`](/docs/sql-reference/data-types/datetime) or [`String`](/docs/sql-reference/data-types/string) or [`(U)Int*`](/docs/sql-reference/data-types/int-uint) or [`Float*`](/docs/sql-reference/data-types/float) or [`Decimal`](/docs/sql-reference/data-types/decimal)

**Returned value**

Returns a UInt64-type number representing the approximate number of different argument values. [`UInt64`](/docs/sql-reference/data-types/int-uint)

**Examples**

**Large dataset example**

```
SELECT uniqCombined64(number) FROM numbers(1e10);
```

```
┌─uniqCombined64(number)─┐
│             9998568925 │
└────────────────────────┘
```

**Comparison with uniqCombined**

```
-- uniqCombined64 with large dataset
SELECT uniqCombined64(number) FROM numbers(1e10);

-- uniqCombined with same dataset shows poor approximation
SELECT uniqCombined(number) FROM numbers(1e10);
```

```
┌─uniqCombined64(number)─┐
│             9998568925 │ -- 10.00 billion
└────────────────────────┘
┌─uniqCombined(number)─┐
│           5545308725 │ -- 5.55 billion
└──────────────────────┘
```

**See Also**

- [uniq](/docs/sql-reference/aggregate-functions/reference/uniq)
- [uniqCombined](/docs/sql-reference/aggregate-functions/reference/uniqcombined)
- [uniqHLL12](/docs/sql-reference/aggregate-functions/reference/uniqhll12)
- [uniqExact](/docs/sql-reference/aggregate-functions/reference/uniqexact)
- [uniqTheta](/docs/sql-reference/aggregate-functions/reference/uniqthetasketch)

- [uniqCombined64](#uniqCombined64)

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