2.2 KiB
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quantileBFloat16
Computes an approximate quantile of a sample consisting of bfloat16 numbers. bfloat16 is a floating-point data type with 1 sign bit, 8 exponent bits and 7 fraction bits.
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.
The function is a fast quantile estimator with a relative error no more than 0.390625%.
Syntax
quantileBFloat16[(level)](expr)
Alias: medianBFloat16
Arguments
Parameters
level— Level of quantile. Optional. Possible values are in the range from 0 to 1. Default value: 0.5. Float.
Returned value
- Approximate quantile of the specified level.
Type: Float64.
Example
Input table has an integer and a float columns:
┌─a─┬─────b─┐
│ 1 │ 1.001 │
│ 2 │ 1.002 │
│ 3 │ 1.003 │
│ 4 │ 1.004 │
└───┴───────┘
Query to calculate 0.75-quantile (third quartile):
SELECT quantileBFloat16(0.75)(a), quantileBFloat16(0.75)(b) FROM example_table;
Result:
┌─quantileBFloat16(0.75)(a)─┬─quantileBFloat16(0.75)(b)─┐
│ 3 │ 1 │
└───────────────────────────┴───────────────────────────┘
Note that all floating point values in the example are truncated to 1.0 when converting to bfloat16.
See Also