ClickHouse/dbms/src/Functions/toLowCardinality.cpp

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#include <Functions/IFunction.h>
#include <Functions/FunctionFactory.h>
#include <DataTypes/DataTypesNumber.h>
#include <DataTypes/DataTypeLowCardinality.h>
#include <Columns/ColumnsNumber.h>
#include <Columns/ColumnLowCardinality.h>
#include <Common/typeid_cast.h>
namespace DB
{
class FunctionToLowCardinality: public IFunction
{
public:
static constexpr auto name = "toLowCardinality";
static FunctionPtr create(const Context &) { return std::make_shared<FunctionToLowCardinality>(); }
String getName() const override { return name; }
size_t getNumberOfArguments() const override { return 1; }
bool useDefaultImplementationForNulls() const override { return false; }
bool useDefaultImplementationForConstants() const override { return true; }
bool useDefaultImplementationForLowCardinalityColumns() const override { return false; }
DataTypePtr getReturnTypeImpl(const DataTypes & arguments) const override
{
if (arguments[0]->lowCardinality())
return arguments[0];
return std::make_shared<DataTypeLowCardinality>(arguments[0]);
}
void executeImpl(Block & block, const ColumnNumbers & arguments, size_t result, size_t /*input_rows_count*/) override
{
auto arg_num = arguments[0];
const auto & arg = block.getByPosition(arg_num);
auto & res = block.getByPosition(result);
if (arg.type->lowCardinality())
res.column = arg.column;
else
{
auto column = res.type->createColumn();
typeid_cast<ColumnLowCardinality &>(*column).insertRangeFromFullColumn(*arg.column, 0, arg.column->size());
res.column = std::move(column);
}
}
};
void registerFunctionToLowCardinality(FunctionFactory & factory)
{
factory.registerFunction<FunctionToLowCardinality>();
}
}