mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-12-11 17:02:25 +00:00
40 lines
1.5 KiB
Markdown
40 lines
1.5 KiB
Markdown
---
|
|
sidebar_position: 190
|
|
---
|
|
|
|
# uniq {#agg_function-uniq}
|
|
|
|
Calculates the approximate number of different values of the argument.
|
|
|
|
``` sql
|
|
uniq(x[, ...])
|
|
```
|
|
|
|
**Arguments**
|
|
|
|
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 does not 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)
|
|
- [uniqTheta](../../../sql-reference/aggregate-functions/reference/uniqthetasketch.md#agg_function-uniqthetasketch)
|