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

#include <Columns/ColumnString.h>
#include <Columns/ColumnsNumber.h>
#include <DataTypes/DataTypeString.h>
#include <DataTypes/DataTypesNumber.h>
#include <DataStreams/OneBlockInputStream.h>
#include <Interpreters/Context.h>
#include <Storages/System/StorageSystemSettings.h>


namespace DB
{


StorageSystemSettings::StorageSystemSettings(const std::string & name_)
    : name(name_)
{
    setColumns(ColumnsDescription({
        { "name",        std::make_shared<DataTypeString>() },
        { "value",       std::make_shared<DataTypeString>() },
        { "changed",     std::make_shared<DataTypeUInt8>() },
        { "description", std::make_shared<DataTypeString>() },
    }));
}


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

    const Settings & settings = context.getSettingsRef();

    MutableColumns res_columns = getSampleBlock().cloneEmptyColumns();

#define ADD_SETTING(TYPE, NAME, DEFAULT, DESCRIPTION) \
    res_columns[0]->insert(String(#NAME)); \
    res_columns[1]->insert(settings.NAME.toString()); \
    res_columns[2]->insert(UInt64(settings.NAME.changed)); \
    res_columns[3]->insert(String(DESCRIPTION));
    APPLY_FOR_SETTINGS(ADD_SETTING)
#undef ADD_SETTING

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


}