ClickHouse/docs/en/sql-reference/aggregate-functions/reference/uniq.md

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# uniq {#agg_function-uniq}

Calculates the approximate number of different values of the argument.

``` sql
uniq(x[, ...])
```

**Parameters**

The function takes a variable number of parameters. Parameters can be `Tuple`, `Array`, `Date`, `DateTime`, `String`, or numeric types.

**Returned value**

-   A [UInt64](../../../sql-reference/data-types/int-uint.md)-type number.

**Implementation details**

Function:

-   Calculates a hash for all parameters in the aggregate, then uses it in calculations.

-   Uses an adaptive sampling algorithm. For the calculation state, the function uses a sample of element hash values up to 65536.

        This algorithm is very accurate and very efficient on the CPU. When the query contains several of these functions, using `uniq` is almost as fast as using other aggregate functions.

-   Provides the result deterministically (it doesn’t depend on the query processing order).

We recommend using this function in almost all scenarios.

**See Also**

-   [uniqCombined](../../../sql-reference/aggregate-functions/reference/uniqcombined.md#agg_function-uniqcombined)
-   [uniqCombined64](../../../sql-reference/aggregate-functions/reference/uniqcombined64.md#agg_function-uniqcombined64)
-   [uniqHLL12](../../../sql-reference/aggregate-functions/reference/uniqhll12.md#agg_function-uniqhll12)
-   [uniqExact](../../../sql-reference/aggregate-functions/reference/uniqexact.md#agg_function-uniqexact)