mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-12-13 09:52:38 +00:00
69 lines
2.7 KiB
Markdown
69 lines
2.7 KiB
Markdown
---
|
||
slug: /en/sql-reference/aggregate-functions/reference/quantileexactweighted
|
||
sidebar_position: 174
|
||
---
|
||
|
||
# quantileExactWeighted
|
||
|
||
Exactly computes the [quantile](https://en.wikipedia.org/wiki/Quantile) of a numeric data sequence, taking into account the weight of each element.
|
||
|
||
To get exact value, all the passed values are combined into an array, which is then partially sorted. Each value is counted with its weight, as if it is present `weight` times. A hash table is used in the algorithm. Because of this, if the passed values are frequently repeated, the function consumes less RAM than [quantileExact](../../../sql-reference/aggregate-functions/reference/quantileexact.md#quantileexact). You can use this function instead of `quantileExact` and specify the weight 1.
|
||
|
||
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.
|
||
|
||
**Syntax**
|
||
|
||
``` sql
|
||
quantileExactWeighted(level)(expr, weight)
|
||
```
|
||
|
||
Alias: `medianExactWeighted`.
|
||
|
||
**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).
|
||
- `weight` — Column with weights of sequence members. Weight is a number of value occurrences.
|
||
|
||
**Returned value**
|
||
|
||
- 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
|
||
┌─n─┬─val─┐
|
||
│ 0 │ 3 │
|
||
│ 1 │ 2 │
|
||
│ 2 │ 1 │
|
||
│ 5 │ 4 │
|
||
└───┴─────┘
|
||
```
|
||
|
||
Query:
|
||
|
||
``` sql
|
||
SELECT quantileExactWeighted(n, val) FROM t
|
||
```
|
||
|
||
Result:
|
||
|
||
``` text
|
||
┌─quantileExactWeighted(n, val)─┐
|
||
│ 1 │
|
||
└───────────────────────────────┘
|
||
```
|
||
|
||
**See Also**
|
||
|
||
- [median](../../../sql-reference/aggregate-functions/reference/median.md#median)
|
||
- [quantiles](../../../sql-reference/aggregate-functions/reference/quantiles.md#quantiles)
|