ClickHouse/src/Functions/namedTupleItems.cpp

#include <Functions/IFunction.h>
#include <Functions/FunctionFactory.h>
#include <Functions/FunctionHelpers.h>
#include <DataTypes/IDataType.h>
#include <DataTypes/DataTypeTuple.h>
#include <DataTypes/DataTypeArray.h>
#include <DataTypes/DataTypeString.h>
#include <Columns/ColumnTuple.h>
#include <Columns/ColumnArray.h>
#include <Columns/ColumnString.h>
#include <Columns/ColumnsNumber.h>
#include <Common/assert_cast.h>
#include <memory>

namespace DB
{
namespace ErrorCodes
{
    extern const int ILLEGAL_TYPE_OF_ARGUMENT;
    extern const int ILLEGAL_INDEX;
}

namespace
{

/** Extract element of tuple by constant index or name. The operation is essentially free.
  * Also the function looks through Arrays: you can get Array of tuple elements from Array of Tuples.
  */
class FunctionNamedTupleItems : public IFunction
{
public:
    static constexpr auto name = "namedTupleItems";
    static FunctionPtr create(ContextPtr)
    {
        return std::make_shared<FunctionNamedTupleItems>();
    }

    String getName() const override
    {
        return name;
    }

    size_t getNumberOfArguments() const override
    {
        return 1;
    }

    bool useDefaultImplementationForConstants() const override
    {
        return true;
    }

    DataTypePtr getReturnTypeImpl(const ColumnsWithTypeAndName & arguments) const override
    {
        // get the type of all the fields in the tuple
        const IDataType * col = arguments[0].type.get();
        const DataTypeTuple * tuple = checkAndGetDataType<DataTypeTuple>(col);

        if (!tuple)
            throw Exception("First argument for function " + getName() + " must "
                            "be a tuple.", ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT);

        const auto& elementTypes = tuple->getElements();

        if (elementTypes.empty())
            throw Exception("The argument tuple for function " + getName() + " must "
                            "not be empty.", ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT);

        const auto& firstElementType = elementTypes[0];

        auto it = std::find_if(
                           elementTypes.begin() + 1,
                           elementTypes.end(),
                           [&](const auto &other)
                           {
                               return !firstElementType->equals(*other);
                           });

        if (it != elementTypes.end())
        {
            throw Exception("The argument tuple for function " + getName() + " must "
                            "contain just one type",
                            ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT);
        }

        DataTypePtr tupleNameType = std::make_shared<DataTypeString>();
        DataTypes itemDataTypes ={tupleNameType,
                                  firstElementType};

        auto itemDataType = std::make_shared<DataTypeTuple>(itemDataTypes);

        return std::make_shared<DataTypeArray>(itemDataType);
    }

    ColumnPtr executeImpl(const ColumnsWithTypeAndName & arguments, const DataTypePtr &, size_t /*input_rows_count*/) const override
    {
        const IColumn *tuple_col = arguments[0].column.get();
        const DataTypeTuple * tuple = checkAndGetDataType<DataTypeTuple>(arguments[0].type.get());
        auto *tuple_col_concrete = assert_cast<const ColumnTuple*>(tuple_col);

        MutableColumnPtr keys = ColumnString::create();
        MutableColumnPtr values = tuple_col_concrete->getColumn(0).cloneEmpty();
        auto offsets = ColumnVector<UInt64>::create();
        for (size_t row = 0; row < tuple_col_concrete->size(); ++row)
        {
            for (size_t col = 0; col < tuple_col_concrete->tupleSize(); ++col)
            {
                const std::string& key = tuple->getElementNames()[col];
                const IColumn& valueColumn = tuple_col_concrete->getColumn(col);

                values->insertFrom(valueColumn, row);
                keys->insertData(key.data(), key.size());
            }
            offsets->insertValue(tuple_col_concrete->tupleSize() * (row + 1));
        }

        std::vector<ColumnPtr> tupleColumns = { std::move(keys), std::move(values) };
        auto tupleColumn = ColumnTuple::create(std::move(tupleColumns));
        return ColumnArray::create(std::move(tupleColumn), std::move(offsets));
    }
};

}

void registerFunctionNamedTupleItems(FunctionFactory & factory)
{
    factory.registerFunction<FunctionNamedTupleItems>();
}

}