ClickHouse/dbms/src/Functions/randConstant.cpp

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#include <Functions/FunctionFactory.h>
#include <Functions/FunctionHelpers.h>
#include <Functions/FunctionsRandom.h>
namespace DB
{
template <typename ToType, typename Name>
class FunctionRandomConstant : public IFunction
{
private:
/// The value is one for different blocks.
bool is_initialized = false;
ToType value;
public:
static constexpr auto name = Name::name;
static FunctionPtr create(const Context &) { return std::make_shared<FunctionRandomConstant>(); }
String getName() const override
{
return name;
}
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
{
if (!is_initialized)
{
is_initialized = true;
typename ColumnVector<ToType>::Container vec_to(1);
RandImpl::execute(reinterpret_cast<char *>(vec_to.data()), sizeof(ToType));
value = vec_to[0];
}
block.getByPosition(result).column = DataTypeNumber<ToType>().createColumnConst(input_rows_count, toField(value));
}
};
struct NameRandConstant { static constexpr auto name = "randConstant"; };
using FunctionRandConstant = FunctionRandomConstant<UInt32, NameRandConstant>;
void registerFunctionRandConstant(FunctionFactory & factory)
{
factory.registerFunction<FunctionRandConstant>();
}
}