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