--- slug: /en/sql-reference/functions/random-functions sidebar_position: 51 sidebar_label: Pseudo-Random Numbers --- # Functions for Generating Pseudo-Random Numbers All the functions accept zero arguments or one argument. If an argument is passed, it can be any type, and its value is not used for anything. The only purpose of this argument is to prevent common subexpression elimination, so that two different instances of the same function return different columns with different random numbers. :::note Non-cryptographic generators of pseudo-random numbers are used. ::: ## rand, rand32 Returns a pseudo-random UInt32 number, evenly distributed among all UInt32-type numbers. Uses a linear congruential generator. ## rand64 Returns a pseudo-random UInt64 number, evenly distributed among all UInt64-type numbers. Uses a linear congruential generator. ## randCanonical The function generates pseudo random results with independent and identically distributed uniformly distributed values in [0, 1). Non-deterministic. Return type is Float64. ## randConstant Produces a constant column with a random value. **Syntax** ``` sql randConstant([x]) ``` **Arguments** - `x` — [Expression](../../sql-reference/syntax.md#syntax-expressions) resulting in any of the [supported data types](../../sql-reference/data-types/index.md#data_types). The resulting value is discarded, but the expression itself if used for bypassing [common subexpression elimination](../../sql-reference/functions/index.md#common-subexpression-elimination) if the function is called multiple times in one query. Optional parameter. **Returned value** - Pseudo-random number. Type: [UInt32](../../sql-reference/data-types/int-uint.md). **Example** Query: ``` sql SELECT rand(), rand(1), rand(number), randConstant(), randConstant(1), randConstant(number) FROM numbers(3) ``` Result: ``` text ┌─────rand()─┬────rand(1)─┬─rand(number)─┬─randConstant()─┬─randConstant(1)─┬─randConstant(number)─┐ │ 3047369878 │ 4132449925 │ 4044508545 │ 2740811946 │ 4229401477 │ 1924032898 │ │ 2938880146 │ 1267722397 │ 4154983056 │ 2740811946 │ 4229401477 │ 1924032898 │ │ 956619638 │ 4238287282 │ 1104342490 │ 2740811946 │ 4229401477 │ 1924032898 │ └────────────┴────────────┴──────────────┴────────────────┴─────────────────┴──────────────────────┘ ``` # Functions for Generating Random Numbers based on Distributions :::note These functions are available starting from 22.10. ::: ## randUniform Return random number based on [continuous uniform distribution](https://en.wikipedia.org/wiki/Continuous_uniform_distribution) in a specified range from `min` to `max`. **Syntax** ``` sql randUniform(min, max) ``` **Arguments** - `min` - `Float64` - min value of the range, - `max` - `Float64` - max value of the range. **Returned value** - Pseudo-random number. Type: [Float64](/docs/en/sql-reference/data-types/float.md). **Example** Query: ``` sql SELECT randUniform(5.5, 10) FROM numbers(5) ``` Result: ``` text ┌─randUniform(5.5, 10)─┐ │ 8.094978491443102 │ │ 7.3181248914450885 │ │ 7.177741903868262 │ │ 6.483347380953762 │ │ 6.122286382885112 │ └──────────────────────┘ ``` ## randNormal Return random number based on [normal distribution](https://en.wikipedia.org/wiki/Normal_distribution). **Syntax** ``` sql randNormal(meam, variance) ``` **Arguments** - `meam` - `Float64` mean value of distribution, - `variance` - `Float64` - [variance](https://en.wikipedia.org/wiki/Variance). **Returned value** - Pseudo-random number. Type: [Float64](/docs/en/sql-reference/data-types/float.md). **Example** Query: ``` sql SELECT randNormal(10, 2) FROM numbers(5) ``` Result: ``` text ┌──randNormal(10, 2)─┐ │ 13.389228911709653 │ │ 8.622949707401295 │ │ 10.801887062682981 │ │ 4.5220192605895315 │ │ 10.901239123982567 │ └────────────────────┘ ``` ## randLogNormal Return random number based on [log-normal distribution](https://en.wikipedia.org/wiki/Log-normal_distribution). **Syntax** ``` sql randLogNormal(meam, variance) ``` **Arguments** - `meam` - `Float64` mean value of distribution, - `variance` - `Float64` - [variance](https://en.wikipedia.org/wiki/Variance). **Returned value** - Pseudo-random number. Type: [Float64](/docs/en/sql-reference/data-types/float.md). **Example** Query: ``` sql SELECT randLogNormal(100, 5) FROM numbers(5) ``` Result: ``` text ┌─randLogNormal(100, 5)─┐ │ 1.295699673937363e48 │ │ 9.719869109186684e39 │ │ 6.110868203189557e42 │ │ 9.912675872925529e39 │ │ 2.3564708490552458e42 │ └───────────────────────┘ ``` ## randBinomial Return random number based on [binomial distribution](https://en.wikipedia.org/wiki/Binomial_distribution). **Syntax** ``` sql randBinomial(experiments, probability) ``` **Arguments** - `experiments` - `UInt64` number of experiments, - `probability` - `Float64` - probability of success in each experiment (values in `0...1` range only). **Returned value** - Pseudo-random number. Type: [UInt64](/docs/en/sql-reference/data-types/int-uint.md). **Example** Query: ``` sql SELECT randBinomial(100, .75) FROM numbers(5) ``` Result: ``` text ┌─randBinomial(100, 0.75)─┐ │ 74 │ │ 78 │ │ 76 │ │ 77 │ │ 80 │ └─────────────────────────┘ ``` ## randNegativeBinomial Return random number based on [negative binomial distribution](https://en.wikipedia.org/wiki/Negative_binomial_distribution). **Syntax** ``` sql randNegativeBinomial(experiments, probability) ``` **Arguments** - `experiments` - `UInt64` number of experiments, - `probability` - `Float64` - probability of failure in each experiment (values in `0...1` range only). **Returned value** - Pseudo-random number. Type: [UInt64](/docs/en/sql-reference/data-types/int-uint.md). **Example** Query: ``` sql SELECT randNegativeBinomial(100, .75) FROM numbers(5) ``` Result: ``` text ┌─randNegativeBinomial(100, 0.75)─┐ │ 33 │ │ 32 │ │ 39 │ │ 40 │ │ 50 │ └─────────────────────────────────┘ ``` ## randPoisson Return random number based on [Poisson distribution](https://en.wikipedia.org/wiki/Poisson_distribution). **Syntax** ``` sql randPoisson(n) ``` **Arguments** - `n` - `UInt64` mean number of occurrences. **Returned value** - Pseudo-random number. Type: [UInt64](/docs/en/sql-reference/data-types/int-uint.md). **Example** Query: ``` sql SELECT randPoisson(10) FROM numbers(5) ``` Result: ``` text ┌─randPoisson(10)─┐ │ 8 │ │ 8 │ │ 7 │ │ 10 │ │ 6 │ └─────────────────┘ ``` ## randBernoulli Return random number based on [Bernoulli distribution](https://en.wikipedia.org/wiki/Bernoulli_distribution). **Syntax** ``` sql randBernoulli(probability) ``` **Arguments** - `probability` - `Float64` - probability of success (values in `0...1` range only). **Returned value** - Pseudo-random number. Type: [UInt64](/docs/en/sql-reference/data-types/int-uint.md). **Example** Query: ``` sql SELECT randBernoulli(.75) FROM numbers(5) ``` Result: ``` text ┌─randBernoulli(0.75)─┐ │ 1 │ │ 1 │ │ 0 │ │ 1 │ │ 1 │ └─────────────────────┘ ``` ## randExponential Return random number based on [exponential distribution](https://en.wikipedia.org/wiki/Exponential_distribution). **Syntax** ``` sql randExponential(lambda) ``` **Arguments** - `lambda` - `Float64` lambda value. **Returned value** - Pseudo-random number. Type: [Float64](/docs/en/sql-reference/data-types/float.md). **Example** Query: ``` sql SELECT randExponential(1/10) FROM numbers(5) ``` Result: ``` text ┌─randExponential(divide(1, 10))─┐ │ 44.71628934340778 │ │ 4.211013337903262 │ │ 10.809402553207766 │ │ 15.63959406553284 │ │ 1.8148392319860158 │ └────────────────────────────────┘ ``` ## randChiSquared Return random number based on [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. **Syntax** ``` sql randChiSquared(degree_of_freedom) ``` **Arguments** - `degree_of_freedom` - `Float64` degree of freedom. **Returned value** - Pseudo-random number. Type: [Float64](/docs/en/sql-reference/data-types/float.md). **Example** Query: ``` sql SELECT randChiSquared(10) FROM numbers(5) ``` Result: ``` text ┌─randChiSquared(10)─┐ │ 10.015463656521543 │ │ 9.621799919882768 │ │ 2.71785015634699 │ │ 11.128188665931908 │ │ 4.902063104425469 │ └────────────────────┘ ``` ## randStudentT Return random number based on [Student's t-distribution](https://en.wikipedia.org/wiki/Student%27s_t-distribution). **Syntax** ``` sql randStudentT(degree_of_freedom) ``` **Arguments** - `degree_of_freedom` - `Float64` degree of freedom. **Returned value** - Pseudo-random number. Type: [Float64](/docs/en/sql-reference/data-types/float.md). **Example** Query: ``` sql SELECT randStudentT(10) FROM numbers(5) ``` Result: ``` text ┌─────randStudentT(10)─┐ │ 1.2217309938538725 │ │ 1.7941971681200541 │ │ -0.28192176076784664 │ │ 0.2508897721303792 │ │ -2.7858432909761186 │ └──────────────────────┘ ``` ## randFisherF Return random number based on [F-distribution](https://en.wikipedia.org/wiki/F-distribution). **Syntax** ``` sql randFisherF(d1, d2) ``` **Arguments** - `d1` - `Float64` d1 degree of freedom in `X = (S1 / d1) / (S2 / d2)`, - `d2` - `Float64` d2 degree of freedom in `X = (S1 / d1) / (S2 / d2)`, **Returned value** - Pseudo-random number. Type: [Float64](/docs/en/sql-reference/data-types/float.md). **Example** Query: ``` sql SELECT randFisherF(10, 3) FROM numbers(5) ``` Result: ``` text ┌──randFisherF(10, 3)─┐ │ 7.286287504216609 │ │ 0.26590779413050386 │ │ 0.22207610901168987 │ │ 0.7953362728449572 │ │ 0.19278885985221572 │ └─────────────────────┘ ``` # Random Functions for Working with Strings ## randomString ## randomFixedString ## randomPrintableASCII ## randomStringUTF8 ## fuzzBits **Syntax** ``` sql fuzzBits([s], [prob]) ``` Inverts bits of `s`, each with probability `prob`. **Arguments** - `s` - `String` or `FixedString` - `prob` - constant `Float32/64` **Returned value** Fuzzed string with same as s type. **Example** ``` sql SELECT fuzzBits(materialize('abacaba'), 0.1) FROM numbers(3) ``` Result: ``` text ┌─fuzzBits(materialize('abacaba'), 0.1)─┐ │ abaaaja │ │ a*cjab+ │ │ aeca2A │ └───────────────────────────────────────┘ ``` ## Related content - Blog: [Generating random data in ClickHouse](https://clickhouse.com/blog/generating-random-test-distribution-data-for-clickhouse)