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#include <Functions/IFunction.h>
#include <Functions/FunctionFactory.h>
#include <DataTypes/DataTypeLowCardinality.h>
#include <Columns/ColumnLowCardinality.h>
#include <Common/typeid_cast.h>
namespace DB
{
namespace
{
class FunctionToLowCardinality: public IFunction
{
public:
static constexpr auto name = "toLowCardinality";
static FunctionPtr create(ContextPtr) { 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; }
bool isSuitableForShortCircuitArgumentsExecution(const DataTypesWithConstInfo & /*arguments*/) const override { return true; }
DataTypePtr getReturnTypeImpl(const DataTypes & arguments) const override
{
if (arguments[0]->lowCardinality())
return arguments[0];
return std::make_shared<DataTypeLowCardinality>(arguments[0]);
}
ColumnPtr executeImpl(const ColumnsWithTypeAndName & arguments, const DataTypePtr & res_type, size_t /*input_rows_count*/) const override
{
const auto & arg = arguments[0];
if (arg.type->lowCardinality())
return arg.column;
else
{
auto column = res_type->createColumn();
typeid_cast<ColumnLowCardinality &>(*column).insertRangeFromFullColumn(*arg.column, 0, arg.column->size());
return column;
}
}
};
}
REGISTER_FUNCTION(ToLowCardinality)
{
factory.registerFunction<FunctionToLowCardinality>();
}
}
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