ClickHouse/dbms/src/Functions/lowCardinalityIndices.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
{
namespace ErrorCodes
{
extern const int ILLEGAL_TYPE_OF_ARGUMENT;
}
class FunctionLowCardinalityIndices: public IFunction
{
public:
static constexpr auto name = "lowCardinalityIndices";
static FunctionPtr create(const Context &) { return std::make_shared<FunctionLowCardinalityIndices>(); }
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
{
auto * type = typeid_cast<const DataTypeLowCardinality *>(arguments[0].get());
if (!type)
throw Exception("First first argument of function lowCardinalityIndexes must be ColumnLowCardinality, but got"
+ arguments[0]->getName(), ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT);
return std::make_shared<DataTypeUInt64>();
}
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);
auto indexes_col = typeid_cast<const ColumnLowCardinality *>(arg.column.get())->getIndexesPtr();
auto new_indexes_col = ColumnUInt64::create(indexes_col->size());
auto & data = new_indexes_col->getData();
for (size_t i = 0; i < data.size(); ++i)
data[i] = indexes_col->getUInt(i);
res.column = std::move(new_indexes_col);
}
};
void registerFunctionLowCardinalityIndices(FunctionFactory & factory)
{
factory.registerFunction<FunctionLowCardinalityIndices>();
}
}