mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-12-03 13:02:00 +00:00
258d2fd499
* normalize
* split & adjust links
* re-normalize
* adjust ru links
* adjust ja/tr links
* partially apply e0d19d2aea
* reset contribs
41 lines
1.4 KiB
Markdown
41 lines
1.4 KiB
Markdown
---
|
||
toc_priority: 190
|
||
---
|
||
|
||
# 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)
|