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69 lines
2.3 KiB
Markdown
69 lines
2.3 KiB
Markdown
---
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slug: /en/sql-reference/aggregate-functions/reference/quantilebfloat16
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sidebar_position: 209
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title: quantileBFloat16
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---
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Computes an approximate [quantile](https://en.wikipedia.org/wiki/Quantile) of a sample consisting of [bfloat16](https://en.wikipedia.org/wiki/Bfloat16_floating-point_format) numbers. `bfloat16` is a floating-point data type with 1 sign bit, 8 exponent bits and 7 fraction bits.
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The function converts input values to 32-bit floats and takes the most significant 16 bits. Then it calculates `bfloat16` quantile value and converts the result to a 64-bit float by appending zero bits.
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The function is a fast quantile estimator with a relative error no more than 0.390625%.
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**Syntax**
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``` sql
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quantileBFloat16[(level)](expr)
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```
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Alias: `medianBFloat16`
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**Arguments**
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- `expr` — Column with numeric data. [Integer](../../../sql-reference/data-types/int-uint.md), [Float](../../../sql-reference/data-types/float.md).
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**Parameters**
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- `level` — Level of quantile. Optional. Possible values are in the range from 0 to 1. Default value: 0.5. [Float](../../../sql-reference/data-types/float.md).
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**Returned value**
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- Approximate quantile of the specified level.
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Type: [Float64](../../../sql-reference/data-types/float.md#float32-float64).
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**Example**
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Input table has an integer and a float columns:
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``` text
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┌─a─┬─────b─┐
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│ 1 │ 1.001 │
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│ 2 │ 1.002 │
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│ 3 │ 1.003 │
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│ 4 │ 1.004 │
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└───┴───────┘
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```
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Query to calculate 0.75-quantile (third quartile):
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``` sql
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SELECT quantileBFloat16(0.75)(a), quantileBFloat16(0.75)(b) FROM example_table;
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```
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Result:
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``` text
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┌─quantileBFloat16(0.75)(a)─┬─quantileBFloat16(0.75)(b)─┐
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│ 3 │ 1 │
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└───────────────────────────┴───────────────────────────┘
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```
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Note that all floating point values in the example are truncated to 1.0 when converting to `bfloat16`.
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# quantileBFloat16Weighted
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Like `quantileBFloat16` but takes into account the weight of each sequence member.
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**See Also**
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- [median](../../../sql-reference/aggregate-functions/reference/median.md#median)
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- [quantiles](../../../sql-reference/aggregate-functions/reference/quantiles.md#quantiles)
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