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

#include <Columns/ColumnString.h>
#include <Columns/ColumnsNumber.h>
#include <DataTypes/DataTypeString.h>
#include <DataTypes/DataTypeDateTime.h>
#include <DataStreams/OneBlockInputStream.h>
#include <Storages/System/StorageSystemTables.h>
#include <Common/VirtualColumnUtils.h>
#include <Databases/IDatabase.h>
#include <Interpreters/Context.h>


namespace DB
{

namespace ErrorCodes
{
    extern const int LOGICAL_ERROR;
}


StorageSystemTables::StorageSystemTables(const std::string & name_)
    : name(name_),
    columns
    {
        {"database",                     std::make_shared<DataTypeString>()},
        {"name",                         std::make_shared<DataTypeString>()},
        {"engine",                        std::make_shared<DataTypeString>()},
        {"metadata_modification_time",    std::make_shared<DataTypeDateTime>()}
    }
{
}


static ColumnWithTypeAndName getFilteredDatabases(const ASTPtr & query, const Context & context)
{
    ColumnWithTypeAndName column;
    column.name = "database";
    column.type = std::make_shared<DataTypeString>();
    column.column = std::make_shared<ColumnString>();

    for (const auto & db : context.getDatabases())
        column.column->insert(db.first);

    Block block;
    block.insert(std::move(column));

    VirtualColumnUtils::filterBlockWithQuery(query, block, context);

    return block.safeGetByPosition(0);
}


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

    Block block;

    ColumnWithTypeAndName col_db;
    col_db.name = "database";
    col_db.type = std::make_shared<DataTypeString>();
    col_db.column = std::make_shared<ColumnString>();
    block.insert(col_db);

    ColumnWithTypeAndName col_name;
    col_name.name = "name";
    col_name.type = std::make_shared<DataTypeString>();
    col_name.column = std::make_shared<ColumnString>();
    block.insert(col_name);

    ColumnWithTypeAndName col_engine;
    col_engine.name = "engine";
    col_engine.type = std::make_shared<DataTypeString>();
    col_engine.column = std::make_shared<ColumnString>();
    block.insert(col_engine);

    ColumnWithTypeAndName col_meta_mod_time;
    col_meta_mod_time.name = "metadata_modification_time";
    col_meta_mod_time.type = std::make_shared<DataTypeDateTime>();
    col_meta_mod_time.column = std::make_shared<ColumnUInt32>();
    block.insert(col_meta_mod_time);

    ColumnWithTypeAndName filtered_databases_column = getFilteredDatabases(query_info.query, context);

    for (size_t row_number = 0; row_number < filtered_databases_column.column->size(); ++row_number)
    {
        std::string database_name = filtered_databases_column.column->getDataAt(row_number).toString();
        auto database = context.tryGetDatabase(database_name);

        if (!database)
        {
            /// Database was deleted just now.
            continue;
        }

        for (auto iterator = database->getIterator(); iterator->isValid(); iterator->next())
        {
            auto table_name = iterator->name();
            col_db.column->insert(database_name);
            col_name.column->insert(table_name);
            col_engine.column->insert(iterator->table()->getName());
            col_meta_mod_time.column->insert(static_cast<UInt64>(database->getTableMetadataModificationTime(table_name)));
        }
    }

    return BlockInputStreams(1, std::make_shared<OneBlockInputStream>(block));
}

}