mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-11-16 20:53:27 +00:00
70 lines
2.4 KiB
Markdown
70 lines
2.4 KiB
Markdown
---
|
|
slug: /en/sql-reference/aggregate-functions/reference/quantile
|
|
sidebar_position: 200
|
|
---
|
|
|
|
# quantile
|
|
|
|
Computes an approximate [quantile](https://en.wikipedia.org/wiki/Quantile) of a numeric data sequence.
|
|
|
|
This function applies [reservoir sampling](https://en.wikipedia.org/wiki/Reservoir_sampling) with a reservoir size up to 8192 and a random number generator for sampling. The result is non-deterministic. To get an exact quantile, use the [quantileExact](../../../sql-reference/aggregate-functions/reference/quantileexact.md#quantileexact) function.
|
|
|
|
When using multiple `quantile*` functions with different levels in a query, the internal states are not combined (that is, the query works less efficiently than it could). In this case, use the [quantiles](../../../sql-reference/aggregate-functions/reference/quantiles.md#quantiles) function.
|
|
|
|
Note that for an empty numeric sequence, `quantile` will return NaN, but its `quantile*` variants will return either NaN or a default value for the sequence type, depending on the variant.
|
|
|
|
**Syntax**
|
|
|
|
``` sql
|
|
quantile(level)(expr)
|
|
```
|
|
|
|
Alias: `median`.
|
|
|
|
**Arguments**
|
|
|
|
- `level` — Level of quantile. Optional parameter. Constant floating-point number from 0 to 1. We recommend using a `level` value in the range of `[0.01, 0.99]`. Default value: 0.5. At `level=0.5` the function calculates [median](https://en.wikipedia.org/wiki/Median).
|
|
- `expr` — Expression over the column values resulting in numeric [data types](../../../sql-reference/data-types/index.md#data_types), [Date](../../../sql-reference/data-types/date.md) or [DateTime](../../../sql-reference/data-types/datetime.md).
|
|
|
|
**Returned value**
|
|
|
|
- Approximate quantile of the specified level.
|
|
|
|
Type:
|
|
|
|
- [Float64](../../../sql-reference/data-types/float.md) for numeric data type input.
|
|
- [Date](../../../sql-reference/data-types/date.md) if input values have the `Date` type.
|
|
- [DateTime](../../../sql-reference/data-types/datetime.md) if input values have the `DateTime` type.
|
|
|
|
**Example**
|
|
|
|
Input table:
|
|
|
|
``` text
|
|
┌─val─┐
|
|
│ 1 │
|
|
│ 1 │
|
|
│ 2 │
|
|
│ 3 │
|
|
└─────┘
|
|
```
|
|
|
|
Query:
|
|
|
|
``` sql
|
|
SELECT quantile(val) FROM t
|
|
```
|
|
|
|
Result:
|
|
|
|
``` text
|
|
┌─quantile(val)─┐
|
|
│ 1.5 │
|
|
└───────────────┘
|
|
```
|
|
|
|
**See Also**
|
|
|
|
- [median](../../../sql-reference/aggregate-functions/reference/median.md#median)
|
|
- [quantiles](../../../sql-reference/aggregate-functions/reference/quantiles.md#quantiles)
|