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.

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.

randConstant

Produces a constant column with a random value.

Syntax

``````randConstant([x])
``````

Arguments

Returned value

• Pseudo-random number.

Type: UInt32.

Example

Query:

``````SELECT rand(), rand(1), rand(number), randConstant(), randConstant(1), randConstant(number)
FROM numbers(3)
``````

Result:

``````┌─────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 │
└────────────┴────────────┴──────────────┴────────────────┴─────────────────┴──────────────────────┘
``````

Random Functions for Working with Strings

fuzzBits

Syntax

``````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

``````SELECT fuzzBits(materialize('abacaba'), 0.1)
FROM numbers(3)
``````

``` text
┌─fuzzBits(materialize(‘abacaba’), 0.1)─┐
│ abaaaja │
│ a*cjab+ │
│ aeca2A │
└───────────────────────────────────────┘