mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-11-18 05:32:52 +00:00
87 lines
2.8 KiB
C++
87 lines
2.8 KiB
C++
#pragma once
|
|
|
|
#include <DataTypes/DataTypesNumber.h>
|
|
#include <Columns/ColumnVector.h>
|
|
#include <Functions/IFunctionImpl.h>
|
|
#include <IO/WriteHelpers.h>
|
|
|
|
|
|
namespace DB
|
|
{
|
|
|
|
namespace ErrorCodes
|
|
{
|
|
extern const int NUMBER_OF_ARGUMENTS_DOESNT_MATCH;
|
|
}
|
|
|
|
/** Pseudo-random number generation functions.
|
|
* The function can be called without arguments or with one argument.
|
|
* The argument is ignored and only serves to ensure that several calls to one function are considered different and do not stick together.
|
|
*
|
|
* Example:
|
|
* SELECT rand(), rand() - will output two identical columns.
|
|
* SELECT rand(1), rand(2) - will output two different columns.
|
|
*
|
|
* Non-cryptographic generators:
|
|
*
|
|
* rand - linear congruential generator 0 .. 2^32 - 1.
|
|
* rand64 - combines several rand values to get values from the range 0 .. 2^64 - 1.
|
|
*
|
|
* randConstant - service function, produces a constant column with a random value.
|
|
*
|
|
* The time is used as the seed.
|
|
* Note: it is reinitialized for each block.
|
|
* This means that the timer must be of sufficient resolution to give different values to each block.
|
|
*/
|
|
|
|
struct RandImpl
|
|
{
|
|
/// Fill memory with random data. The memory region must be 15-bytes padded.
|
|
static void execute(char * output, size_t size);
|
|
};
|
|
|
|
|
|
template <typename ToType, typename Name>
|
|
class FunctionRandom : public IFunction
|
|
{
|
|
public:
|
|
static constexpr auto name = Name::name;
|
|
static FunctionPtr create(const Context &) { return std::make_shared<FunctionRandom>(); }
|
|
|
|
String getName() const override
|
|
{
|
|
return name;
|
|
}
|
|
|
|
bool isDeterministic() const override { return false; }
|
|
bool isDeterministicInScopeOfQuery() const override { return false; }
|
|
bool useDefaultImplementationForNulls() const override { return false; }
|
|
|
|
bool isVariadic() const override { return true; }
|
|
size_t getNumberOfArguments() const override { return 0; }
|
|
|
|
DataTypePtr getReturnTypeImpl(const DataTypes & arguments) const override
|
|
{
|
|
if (arguments.size() > 1)
|
|
throw Exception("Number of arguments for function " + getName() + " doesn't match: passed "
|
|
+ toString(arguments.size()) + ", should be 0 or 1.",
|
|
ErrorCodes::NUMBER_OF_ARGUMENTS_DOESNT_MATCH);
|
|
|
|
return std::make_shared<DataTypeNumber<ToType>>();
|
|
}
|
|
|
|
void executeImpl(Block & block, const ColumnNumbers &, size_t result, size_t input_rows_count) override
|
|
{
|
|
auto col_to = ColumnVector<ToType>::create();
|
|
typename ColumnVector<ToType>::Container & vec_to = col_to->getData();
|
|
|
|
size_t size = input_rows_count;
|
|
vec_to.resize(size);
|
|
RandImpl::execute(reinterpret_cast<char *>(vec_to.data()), vec_to.size() * sizeof(ToType));
|
|
|
|
block.getByPosition(result).column = std::move(col_to);
|
|
}
|
|
};
|
|
|
|
}
|