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Markdown
666 lines
15 KiB
Markdown
---
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slug: /en/sql-reference/functions/random-functions
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sidebar_position: 145
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sidebar_label: Random Numbers
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---
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# Functions for Generating Random Numbers
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All functions in this section accept zero or one arguments. The only use of the argument (if provided) is to prevent [common subexpression
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elimination](../../sql-reference/functions/index.md#common-subexpression-elimination) such that two different executions within a row of the same random
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function return different random values.
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Related content
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- Blog: [Generating random data in ClickHouse](https://clickhouse.com/blog/generating-random-test-distribution-data-for-clickhouse)
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:::note
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The random numbers are generated by non-cryptographic algorithms.
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:::
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## rand, rand32
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Returns a random UInt32 number, evenly distributed across the range of all possible UInt32 numbers.
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Uses a linear congruential generator.
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## rand64
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Returns a random UInt64 number, evenly distributed across the range of all possible UInt64 numbers.
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Uses a linear congruential generator.
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## randCanonical
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Returns a random Float64 value, evenly distributed in interval [0, 1).
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## randConstant
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Like `rand` but produces a constant column with a random value.
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**Example**
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``` sql
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SELECT rand(), rand(1), rand(number), randConstant(), randConstant(1), randConstant(number)
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FROM numbers(3)
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```
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Result:
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``` result
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┌─────rand()─┬────rand(1)─┬─rand(number)─┬─randConstant()─┬─randConstant(1)─┬─randConstant(number)─┐
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│ 3047369878 │ 4132449925 │ 4044508545 │ 2740811946 │ 4229401477 │ 1924032898 │
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│ 2938880146 │ 1267722397 │ 4154983056 │ 2740811946 │ 4229401477 │ 1924032898 │
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│ 956619638 │ 4238287282 │ 1104342490 │ 2740811946 │ 4229401477 │ 1924032898 │
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└────────────┴────────────┴──────────────┴────────────────┴─────────────────┴──────────────────────┘
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```
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## randUniform
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Returns a random Float64 drawn uniformly from interval [`min`, `max`) ([continuous uniform distribution](https://en.wikipedia.org/wiki/Continuous_uniform_distribution)).
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**Syntax**
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``` sql
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randUniform(min, max)
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```
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**Arguments**
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- `min` - `Float64` - left boundary of the range,
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- `max` - `Float64` - right boundary of the range.
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**Returned value**
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- Random number.
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Type: [Float64](/docs/en/sql-reference/data-types/float.md).
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**Example**
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``` sql
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SELECT randUniform(5.5, 10) FROM numbers(5)
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```
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Result:
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``` result
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┌─randUniform(5.5, 10)─┐
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│ 8.094978491443102 │
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│ 7.3181248914450885 │
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│ 7.177741903868262 │
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│ 6.483347380953762 │
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│ 6.122286382885112 │
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└──────────────────────┘
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```
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## randNormal
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Returns a random Float64 drawn from a [normal distribution](https://en.wikipedia.org/wiki/Normal_distribution).
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**Syntax**
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``` sql
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randNormal(mean, variance)
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```
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**Arguments**
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- `mean` - `Float64` - mean value of distribution,
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- `variance` - `Float64` - [variance](https://en.wikipedia.org/wiki/Variance) of the distribution.
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**Returned value**
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- Random number.
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Type: [Float64](/docs/en/sql-reference/data-types/float.md).
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**Example**
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``` sql
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SELECT randNormal(10, 2) FROM numbers(5)
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```
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Result:
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``` result
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┌──randNormal(10, 2)─┐
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│ 13.389228911709653 │
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│ 8.622949707401295 │
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│ 10.801887062682981 │
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│ 4.5220192605895315 │
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│ 10.901239123982567 │
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└────────────────────┘
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```
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## randLogNormal
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Returns a random Float64 drawn from a [log-normal distribution](https://en.wikipedia.org/wiki/Log-normal_distribution).
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**Syntax**
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``` sql
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randLogNormal(mean, variance)
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```
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**Arguments**
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- `mean` - `Float64` - mean value of distribution,
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- `variance` - `Float64` - [variance](https://en.wikipedia.org/wiki/Variance) of the distribution.
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**Returned value**
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- Random number.
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Type: [Float64](/docs/en/sql-reference/data-types/float.md).
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**Example**
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``` sql
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SELECT randLogNormal(100, 5) FROM numbers(5)
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```
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Result:
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``` result
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┌─randLogNormal(100, 5)─┐
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│ 1.295699673937363e48 │
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│ 9.719869109186684e39 │
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│ 6.110868203189557e42 │
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│ 9.912675872925529e39 │
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│ 2.3564708490552458e42 │
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└───────────────────────┘
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```
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## randBinomial
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Returns a random UInt64 drawn from a [binomial distribution](https://en.wikipedia.org/wiki/Binomial_distribution).
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**Syntax**
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``` sql
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randBinomial(experiments, probability)
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```
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**Arguments**
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- `experiments` - `UInt64` - number of experiments,
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- `probability` - `Float64` - probability of success in each experiment, a value between 0 and 1.
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**Returned value**
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- Random number.
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Type: [UInt64](/docs/en/sql-reference/data-types/int-uint.md).
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**Example**
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``` sql
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SELECT randBinomial(100, .75) FROM numbers(5)
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```
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Result:
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``` result
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┌─randBinomial(100, 0.75)─┐
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│ 74 │
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│ 78 │
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│ 76 │
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│ 77 │
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│ 80 │
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└─────────────────────────┘
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```
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## randNegativeBinomial
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Returns a random UInt64 drawn from a [negative binomial distribution](https://en.wikipedia.org/wiki/Negative_binomial_distribution).
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**Syntax**
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``` sql
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randNegativeBinomial(experiments, probability)
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```
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**Arguments**
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- `experiments` - `UInt64` - number of experiments,
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- `probability` - `Float64` - probability of failure in each experiment, a value between 0 and 1.
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**Returned value**
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- Random number.
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Type: [UInt64](/docs/en/sql-reference/data-types/int-uint.md).
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**Example**
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``` sql
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SELECT randNegativeBinomial(100, .75) FROM numbers(5)
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```
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Result:
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``` result
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┌─randNegativeBinomial(100, 0.75)─┐
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│ 33 │
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│ 32 │
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│ 39 │
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│ 40 │
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│ 50 │
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└─────────────────────────────────┘
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```
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## randPoisson
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Returns a random UInt64 drawn from a [Poisson distribution](https://en.wikipedia.org/wiki/Poisson_distribution).
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**Syntax**
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``` sql
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randPoisson(n)
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```
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**Arguments**
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- `n` - `UInt64` - mean number of occurrences.
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**Returned value**
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- Random number.
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Type: [UInt64](/docs/en/sql-reference/data-types/int-uint.md).
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**Example**
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``` sql
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SELECT randPoisson(10) FROM numbers(5)
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```
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Result:
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``` result
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┌─randPoisson(10)─┐
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│ 8 │
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│ 8 │
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│ 7 │
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│ 10 │
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│ 6 │
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└─────────────────┘
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```
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## randBernoulli
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Returns a random UInt64 drawn from a [Bernoulli distribution](https://en.wikipedia.org/wiki/Bernoulli_distribution).
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**Syntax**
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``` sql
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randBernoulli(probability)
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```
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**Arguments**
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- `probability` - `Float64` - probability of success, a value between 0 and 1.
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**Returned value**
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- Random number.
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Type: [UInt64](/docs/en/sql-reference/data-types/int-uint.md).
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**Example**
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``` sql
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SELECT randBernoulli(.75) FROM numbers(5)
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```
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Result:
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``` result
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┌─randBernoulli(0.75)─┐
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│ 1 │
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│ 1 │
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│ 0 │
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│ 1 │
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│ 1 │
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└─────────────────────┘
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```
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## randExponential
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Returns a random Float64 drawn from a [exponential distribution](https://en.wikipedia.org/wiki/Exponential_distribution).
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**Syntax**
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``` sql
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randExponential(lambda)
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```
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**Arguments**
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- `lambda` - `Float64` - lambda value.
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**Returned value**
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- Random number.
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Type: [Float64](/docs/en/sql-reference/data-types/float.md).
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**Example**
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``` sql
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SELECT randExponential(1/10) FROM numbers(5)
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```
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Result:
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``` result
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┌─randExponential(divide(1, 10))─┐
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│ 44.71628934340778 │
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│ 4.211013337903262 │
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│ 10.809402553207766 │
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│ 15.63959406553284 │
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│ 1.8148392319860158 │
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└────────────────────────────────┘
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```
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## randChiSquared
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Returns a random Float64 drawn from a [Chi-square distribution](https://en.wikipedia.org/wiki/Chi-squared_distribution) - a distribution of a sum of the squares of k independent standard normal random variables.
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**Syntax**
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``` sql
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randChiSquared(degree_of_freedom)
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```
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**Arguments**
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- `degree_of_freedom` - `Float64` - degree of freedom.
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**Returned value**
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- Random number.
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Type: [Float64](/docs/en/sql-reference/data-types/float.md).
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**Example**
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``` sql
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SELECT randChiSquared(10) FROM numbers(5)
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```
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Result:
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``` result
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┌─randChiSquared(10)─┐
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│ 10.015463656521543 │
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│ 9.621799919882768 │
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│ 2.71785015634699 │
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│ 11.128188665931908 │
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│ 4.902063104425469 │
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└────────────────────┘
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```
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## randStudentT
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Returns a random Float64 drawn from a [Student's t-distribution](https://en.wikipedia.org/wiki/Student%27s_t-distribution).
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**Syntax**
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``` sql
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randStudentT(degree_of_freedom)
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```
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**Arguments**
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- `degree_of_freedom` - `Float64` - degree of freedom.
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**Returned value**
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- Random number.
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Type: [Float64](/docs/en/sql-reference/data-types/float.md).
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**Example**
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``` sql
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SELECT randStudentT(10) FROM numbers(5)
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```
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Result:
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``` result
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┌─────randStudentT(10)─┐
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│ 1.2217309938538725 │
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│ 1.7941971681200541 │
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│ -0.28192176076784664 │
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│ 0.2508897721303792 │
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│ -2.7858432909761186 │
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└──────────────────────┘
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```
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## randFisherF
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Returns a random Float64 drawn from a [F-distribution](https://en.wikipedia.org/wiki/F-distribution).
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**Syntax**
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``` sql
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randFisherF(d1, d2)
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```
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**Arguments**
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- `d1` - `Float64` - d1 degree of freedom in `X = (S1 / d1) / (S2 / d2)`,
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- `d2` - `Float64` - d2 degree of freedom in `X = (S1 / d1) / (S2 / d2)`,
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**Returned value**
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- Random number.
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Type: [Float64](/docs/en/sql-reference/data-types/float.md).
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**Example**
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``` sql
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SELECT randFisherF(10, 3) FROM numbers(5)
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```
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Result:
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``` result
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┌──randFisherF(10, 3)─┐
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│ 7.286287504216609 │
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│ 0.26590779413050386 │
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│ 0.22207610901168987 │
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│ 0.7953362728449572 │
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│ 0.19278885985221572 │
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└─────────────────────┘
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```
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## randomString {#randomString}
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Generates a string of the specified length filled with random bytes (including zero bytes). Not all characters may be printable.
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**Syntax**
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``` sql
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randomString(length)
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```
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**Arguments**
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- `length` — String length in bytes. Positive integer.
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**Returned value**
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- String filled with random bytes.
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Type: [String](../../sql-reference/data-types/string.md).
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**Example**
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Query:
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``` sql
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SELECT randomString(30) AS str, length(str) AS len FROM numbers(2) FORMAT Vertical;
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```
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Result:
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``` text
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Row 1:
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──────
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str: 3 G : pT ?w тi k aV f6
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len: 30
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Row 2:
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──────
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str: 9 ,] ^ ) ]?? 8
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len: 30
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```
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## randomFixedString
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Generates a binary string of the specified length filled with random bytes (including zero bytes). Not all characters may be printable.
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**Syntax**
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``` sql
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randomFixedString(length);
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```
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**Arguments**
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- `length` — String length in bytes. [UInt64](../../sql-reference/data-types/int-uint.md).
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**Returned value(s)**
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- String filled with random bytes.
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Type: [FixedString](../../sql-reference/data-types/fixedstring.md).
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**Example**
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Query:
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```sql
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SELECT randomFixedString(13) as rnd, toTypeName(rnd)
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```
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Result:
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```text
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┌─rnd──────┬─toTypeName(randomFixedString(13))─┐
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│ j▒h㋖HɨZ'▒ │ FixedString(13) │
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└──────────┴───────────────────────────────────┘
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```
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## randomPrintableASCII
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Generates a string with a random set of [ASCII](https://en.wikipedia.org/wiki/ASCII#Printable_characters) characters. All characters are printable.
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If you pass `length < 0`, the behavior of the function is undefined.
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**Syntax**
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``` sql
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randomPrintableASCII(length)
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```
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**Arguments**
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- `length` — String length in bytes. Positive integer.
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**Returned value**
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- String with a random set of [ASCII](https://en.wikipedia.org/wiki/ASCII#Printable_characters) printable characters.
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Type: [String](../../sql-reference/data-types/string.md)
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**Example**
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``` sql
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SELECT number, randomPrintableASCII(30) as str, length(str) FROM system.numbers LIMIT 3
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```
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``` text
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┌─number─┬─str────────────────────────────┬─length(randomPrintableASCII(30))─┐
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│ 0 │ SuiCOSTvC0csfABSw=UcSzp2.`rv8x │ 30 │
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│ 1 │ 1Ag NlJ &RCN:*>HVPG;PE-nO"SUFD │ 30 │
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│ 2 │ /"+<"wUTh:=LjJ Vm!c&hI*m#XTfzz │ 30 │
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└────────┴────────────────────────────────┴──────────────────────────────────┘
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```
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## randomStringUTF8
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Generates a random string of a specified length. Result string contains valid UTF-8 code points. The value of code points may be outside of the range of assigned Unicode.
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**Syntax**
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``` sql
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randomStringUTF8(length);
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```
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**Arguments**
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- `length` — Length of the string in code points. [UInt64](../../sql-reference/data-types/int-uint.md).
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**Returned value(s)**
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- UTF-8 random string.
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Type: [String](../../sql-reference/data-types/string.md).
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**Example**
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Query:
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|
|
```sql
|
|
SELECT randomStringUTF8(13)
|
|
```
|
|
|
|
Result:
|
|
|
|
```text
|
|
┌─randomStringUTF8(13)─┐
|
|
│ 𘤗д兠庇 │
|
|
└──────────────────────┘
|
|
```
|
|
|
|
## fuzzBits {#fuzzBits}
|
|
|
|
**Syntax**
|
|
|
|
Flips the bits of String or FixedString `s`, each with probability `prob`.
|
|
|
|
**Syntax**
|
|
|
|
``` sql
|
|
fuzzBits(s, prob)
|
|
```
|
|
|
|
**Arguments**
|
|
- `s` - `String` or `FixedString`,
|
|
- `prob` - constant `Float32/64` between 0.0 and 1.0.
|
|
|
|
**Returned value**
|
|
|
|
Fuzzed string with same type as `s`.
|
|
|
|
**Example**
|
|
|
|
``` sql
|
|
SELECT fuzzBits(materialize('abacaba'), 0.1)
|
|
FROM numbers(3)
|
|
```
|
|
|
|
Result:
|
|
|
|
``` result
|
|
┌─fuzzBits(materialize('abacaba'), 0.1)─┐
|
|
│ abaaaja │
|
|
│ a*cjab+ │
|
|
│ aeca2A │
|
|
└───────────────────────────────────────┘
|
|
```
|