ClickHouse/dbms/src/Storages/System/StorageSystemFunctions.cpp

#include <Storages/System/StorageSystemFunctions.h>
#include <Functions/FunctionFactory.h>
#include <Functions/IFunction.h>
#include <AggregateFunctions/AggregateFunctionFactory.h>
#include <Columns/ColumnString.h>
#include <Columns/ColumnsNumber.h>
#include <DataTypes/DataTypeString.h>
#include <DataTypes/DataTypesNumber.h>
#include <DataStreams/OneBlockInputStream.h>
#include <Interpreters/Context.h>


namespace DB
{

StorageSystemFunctions::StorageSystemFunctions(const std::string & name_)
    : name(name_)
{
    columns = ColumnsDescription({
        { "name",         std::make_shared<DataTypeString>() },
        { "is_aggregate", std::make_shared<DataTypeUInt8>()  },
    });
}


BlockInputStreams StorageSystemFunctions::read(
    const Names & column_names,
    const SelectQueryInfo &,
    const Context &,
    QueryProcessingStage::Enum & processed_stage,
    const size_t /*max_block_size*/,
    const unsigned /*num_streams*/)
{
    check(column_names);
    processed_stage = QueryProcessingStage::FetchColumns;

    MutableColumns res_columns = getSampleBlock().cloneEmptyColumns();

    const auto & functions = FunctionFactory::instance().functions;
    for (const auto & it : functions)
    {
        res_columns[0]->insert(it.first);
        res_columns[1]->insert(UInt64(0));
    }

    const auto & aggregate_functions = AggregateFunctionFactory::instance().aggregate_functions;
    for (const auto & it : aggregate_functions)
    {
        res_columns[0]->insert(it.first);
        res_columns[1]->insert(UInt64(1));
    }

    return BlockInputStreams(1, std::make_shared<OneBlockInputStream>(getSampleBlock().cloneWithColumns(std::move(res_columns))));
}

}