ClickHouse/dbms/src/Interpreters/InterpreterCreateQuery.cpp

#include <memory>

#include <Poco/File.h>

#include <Common/StringUtils/StringUtils.h>
#include <Common/escapeForFileName.h>
#include <Common/typeid_cast.h>

#include <IO/WriteBufferFromFile.h>
#include <IO/WriteHelpers.h>

#include <Parsers/ASTColumnDeclaration.h>
#include <Parsers/ASTCreateQuery.h>
#include <Parsers/ASTIdentifier.h>
#include <Parsers/ASTIndexDeclaration.h>
#include <Parsers/ASTLiteral.h>
#include <Parsers/ASTNameTypePair.h>
#include <Parsers/ASTInsertQuery.h>
#include <Parsers/ParserCreateQuery.h>
#include <Parsers/formatAST.h>
#include <Parsers/parseQuery.h>

#include <Storages/StorageFactory.h>

#include <Interpreters/Context.h>
#include <Interpreters/DDLWorker.h>
#include <Interpreters/ExpressionAnalyzer.h>
#include <Interpreters/SyntaxAnalyzer.h>
#include <Interpreters/InterpreterCreateQuery.h>
#include <Interpreters/InterpreterSelectWithUnionQuery.h>
#include <Interpreters/InterpreterInsertQuery.h>
#include <Interpreters/ExpressionActions.h>
#include <Interpreters/AddDefaultDatabaseVisitor.h>

#include <DataTypes/DataTypeFactory.h>
#include <DataTypes/NestedUtils.h>
#include <DataTypes/DataTypesNumber.h>
#include <DataTypes/DataTypeLowCardinality.h>
#include <DataTypes/DataTypeNullable.h>

#include <Databases/DatabaseFactory.h>
#include <Databases/IDatabase.h>

#include <Compression/CompressionFactory.h>

#include <Interpreters/InterpreterDropQuery.h>
#include <Interpreters/addTypeConversionToAST.h>

#include <TableFunctions/TableFunctionFactory.h>

#include <boost/uuid/uuid_generators.hpp>
#include <boost/uuid/uuid_io.hpp>

namespace DB
{

namespace ErrorCodes
{
    extern const int TABLE_ALREADY_EXISTS;
    extern const int EMPTY_LIST_OF_COLUMNS_PASSED;
    extern const int INCORRECT_QUERY;
    extern const int ENGINE_REQUIRED;
    extern const int UNKNOWN_DATABASE_ENGINE;
    extern const int DUPLICATE_COLUMN;
    extern const int READONLY;
    extern const int ILLEGAL_COLUMN;
    extern const int DATABASE_ALREADY_EXISTS;
    extern const int QUERY_IS_PROHIBITED;
    extern const int THERE_IS_NO_DEFAULT_VALUE;
    extern const int BAD_DATABASE_FOR_TEMPORARY_TABLE;
    extern const int SUSPICIOUS_TYPE_FOR_LOW_CARDINALITY;
    extern const int DICTIONARY_ALREADY_EXISTS;
}


InterpreterCreateQuery::InterpreterCreateQuery(const ASTPtr & query_ptr_, Context & context_)
    : query_ptr(query_ptr_), context(context_)
{
}


BlockIO InterpreterCreateQuery::createDatabase(ASTCreateQuery & create)
{
    if (!create.cluster.empty())
        return executeDDLQueryOnCluster(query_ptr, context, {create.database});

    String database_name = create.database;

    auto guard = context.getDDLGuard(database_name, "");

    /// Database can be created before or it can be created concurrently in another thread, while we were waiting in DDLGuard
    if (context.isDatabaseExist(database_name))
    {
        if (create.if_not_exists)
            return {};
        else
            throw Exception("Database " + database_name + " already exists.", ErrorCodes::DATABASE_ALREADY_EXISTS);
    }

    if (!create.storage)
    {
        /// For new-style databases engine is explicitly specified in .sql
        /// When attaching old-style database during server startup, we must always use Ordinary engine
        //FIXME is it possible, that database engine is not specified in metadata file?
        if (create.attach)
            throw Exception("Database engine must be specified for ATTACH DATABASE query", ErrorCodes::UNKNOWN_DATABASE_ENGINE);
        bool old_style_database = context.getSettingsRef().default_database_engine.value == DefaultDatabaseEngine::Ordinary;
        auto engine = std::make_shared<ASTFunction>();
        auto storage = std::make_shared<ASTStorage>();
        engine->name = old_style_database ? "Ordinary" : "Atomic";
        storage->set(storage->engine, engine);
        create.set(create.storage, storage);

        if (database_name == "datasets")
        {
            //FIXME it's just to run stateful and stress tests without updating docker images
            engine->name = "Ordinary";
        }
    }
    else if ((create.columns_list && create.columns_list->indices && !create.columns_list->indices->children.empty()))
    {
        /// Currently, there are no database engines, that support any arguments.
        std::stringstream ostr;
        formatAST(*create.storage, ostr, false, false);
        throw Exception("Unknown database engine: " + ostr.str(), ErrorCodes::UNKNOWN_DATABASE_ENGINE);
    }


    String database_name_escaped = escapeForFileName(database_name);
    String path = context.getPath();
    String metadata_path = path + "metadata/" + database_name_escaped + "/";

    DatabasePtr database = DatabaseFactory::get(database_name, metadata_path, create.storage, context);

    /// Will write file with database metadata, if needed.
    String metadata_file_tmp_path = path + "metadata/" + database_name_escaped + ".sql.tmp";
    String metadata_file_path = path + "metadata/" + database_name_escaped + ".sql";

    bool need_write_metadata = !create.attach;

    if (need_write_metadata)
    {
        create.attach = true;
        create.if_not_exists = false;

        std::ostringstream statement_stream;
        formatAST(create, statement_stream, false);
        statement_stream << '\n';
        String statement = statement_stream.str();

        /// Exclusive flag guarantees, that database is not created right now in another thread.
        WriteBufferFromFile out(metadata_file_tmp_path, statement.size(), O_WRONLY | O_CREAT | O_EXCL);
        writeString(statement, out);

        out.next();
        if (context.getSettingsRef().fsync_metadata)
            out.sync();
        out.close();
    }

    bool added = false;
    bool renamed = false;
    try
    {
        context.addDatabase(database_name, database);
        added = true;

        if (need_write_metadata)
        {
            Poco::File(metadata_file_tmp_path).renameTo(metadata_file_path);
            renamed = true;
        }

        database->loadStoredObjects(context, has_force_restore_data_flag);
    }
    catch (...)
    {
        if (renamed)
            Poco::File(metadata_file_tmp_path).remove();
        if (added)
            context.detachDatabase(database_name);

        throw;
    }

    return {};
}


ASTPtr InterpreterCreateQuery::formatColumns(const NamesAndTypesList & columns)
{
    auto columns_list = std::make_shared<ASTExpressionList>();

    for (const auto & column : columns)
    {
        const auto column_declaration = std::make_shared<ASTColumnDeclaration>();
        column_declaration->name = column.name;

        ParserIdentifierWithOptionalParameters storage_p;
        String type_name = column.type->getName();
        auto pos = type_name.data();
        const auto end = pos + type_name.size();
        column_declaration->type = parseQuery(storage_p, pos, end, "data type", 0);
        columns_list->children.emplace_back(column_declaration);
    }

    return columns_list;
}

ASTPtr InterpreterCreateQuery::formatColumns(const ColumnsDescription & columns)
{
    auto columns_list = std::make_shared<ASTExpressionList>();

    for (const auto & column : columns)
    {
        /// Do not include virtual columns
        if (column.is_virtual)
            continue;

        const auto column_declaration = std::make_shared<ASTColumnDeclaration>();
        ASTPtr column_declaration_ptr{column_declaration};

        column_declaration->name = column.name;

        ParserIdentifierWithOptionalParameters storage_p;
        String type_name = column.type->getName();
        auto type_name_pos = type_name.data();
        const auto type_name_end = type_name_pos + type_name.size();
        column_declaration->type = parseQuery(storage_p, type_name_pos, type_name_end, "data type", 0);

        if (column.default_desc.expression)
        {
            column_declaration->default_specifier = toString(column.default_desc.kind);
            column_declaration->default_expression = column.default_desc.expression->clone();
        }

        if (!column.comment.empty())
        {
            column_declaration->comment = std::make_shared<ASTLiteral>(Field(column.comment));
        }

        if (column.codec)
        {
            String codec_desc = column.codec->getCodecDesc();
            codec_desc = "CODEC(" + codec_desc + ")";
            auto codec_desc_pos = codec_desc.data();
            const auto codec_desc_end = codec_desc_pos + codec_desc.size();
            ParserIdentifierWithParameters codec_p;
            column_declaration->codec = parseQuery(codec_p, codec_desc_pos, codec_desc_end, "column codec", 0);
        }

        if (column.ttl)
            column_declaration->ttl = column.ttl;

        columns_list->children.push_back(column_declaration_ptr);
    }

    return columns_list;
}

ASTPtr InterpreterCreateQuery::formatIndices(const IndicesDescription & indices)
{
    auto res = std::make_shared<ASTExpressionList>();

    for (const auto & index : indices.indices)
        res->children.push_back(index->clone());

    return res;
}

ASTPtr InterpreterCreateQuery::formatConstraints(const ConstraintsDescription & constraints)
{
    auto res = std::make_shared<ASTExpressionList>();

    for (const auto & constraint : constraints.constraints)
        res->children.push_back(constraint->clone());

    return res;
}

ColumnsDescription InterpreterCreateQuery::getColumnsDescription(const ASTExpressionList & columns_ast, const Context & context)
{
    /// First, deduce implicit types.

    /** all default_expressions as a single expression list,
     *  mixed with conversion-columns for each explicitly specified type */
    ASTPtr default_expr_list = std::make_shared<ASTExpressionList>();
    NamesAndTypesList column_names_and_types;

    for (const auto & ast : columns_ast.children)
    {
        const auto & col_decl = ast->as<ASTColumnDeclaration &>();

        DataTypePtr column_type = nullptr;
        if (col_decl.type)
        {
            column_type = DataTypeFactory::instance().get(col_decl.type);
            column_names_and_types.emplace_back(col_decl.name, column_type);
        }
        else
        {
            /// we're creating dummy DataTypeUInt8 in order to prevent the NullPointerException in ExpressionActions
            column_names_and_types.emplace_back(col_decl.name, std::make_shared<DataTypeUInt8>());
        }

        /// add column to postprocessing if there is a default_expression specified
        if (col_decl.default_expression)
        {
            /** For columns with explicitly-specified type create two expressions:
              * 1. default_expression aliased as column name with _tmp suffix
              * 2. conversion of expression (1) to explicitly-specified type alias as column name
              */
            if (col_decl.type)
            {
                const auto & final_column_name = col_decl.name;
                const auto tmp_column_name = final_column_name + "_tmp";
                const auto data_type_ptr = column_names_and_types.back().type.get();


                default_expr_list->children.emplace_back(
                    setAlias(addTypeConversionToAST(std::make_shared<ASTIdentifier>(tmp_column_name), data_type_ptr->getName()),
                        final_column_name));

                default_expr_list->children.emplace_back(
                    setAlias(
                        col_decl.default_expression->clone(),
                        tmp_column_name));
            }
            else
                default_expr_list->children.emplace_back(setAlias(col_decl.default_expression->clone(), col_decl.name));
        }
    }

    Block defaults_sample_block;
    /// set missing types and wrap default_expression's in a conversion-function if necessary
    if (!default_expr_list->children.empty())
    {
        auto syntax_analyzer_result = SyntaxAnalyzer(context).analyze(default_expr_list, column_names_and_types);
        const auto actions = ExpressionAnalyzer(default_expr_list, syntax_analyzer_result, context).getActions(true);
        for (auto action : actions->getActions())
            if (action.type == ExpressionAction::Type::JOIN || action.type == ExpressionAction::Type::ARRAY_JOIN)
                throw Exception("Cannot CREATE table. Unsupported default value that requires ARRAY JOIN or JOIN action", ErrorCodes::THERE_IS_NO_DEFAULT_VALUE);

        defaults_sample_block = actions->getSampleBlock();
    }

    ColumnsDescription res;
    auto name_type_it = column_names_and_types.begin();
    for (auto ast_it = columns_ast.children.begin(); ast_it != columns_ast.children.end(); ++ast_it, ++name_type_it)
    {
        ColumnDescription column;

        auto & col_decl = (*ast_it)->as<ASTColumnDeclaration &>();

        column.name = col_decl.name;

        if (col_decl.default_expression)
        {
            ASTPtr default_expr = col_decl.default_expression->clone();
            if (col_decl.type)
            {
                const auto & deduced_type = defaults_sample_block.getByName(column.name + "_tmp").type;
                column.type = name_type_it->type;

                if (!column.type->equals(*deduced_type))
                    default_expr = addTypeConversionToAST(std::move(default_expr), column.type->getName());
            }
            else
                column.type = defaults_sample_block.getByName(column.name).type;

            column.default_desc.kind = columnDefaultKindFromString(col_decl.default_specifier);
            column.default_desc.expression = default_expr;
        }
        else if (col_decl.type)
            column.type = name_type_it->type;
        else
            throw Exception();

        if (col_decl.comment)
            column.comment = col_decl.comment->as<ASTLiteral &>().value.get<String>();

        if (col_decl.codec)
            column.codec = CompressionCodecFactory::instance().get(col_decl.codec, column.type);

        if (col_decl.ttl)
            column.ttl = col_decl.ttl;

        res.add(std::move(column));
    }

    res.flattenNested();

    if (res.getAllPhysical().empty())
        throw Exception{"Cannot CREATE table without physical columns", ErrorCodes::EMPTY_LIST_OF_COLUMNS_PASSED};

    return res;
}


ConstraintsDescription InterpreterCreateQuery::getConstraintsDescription(const ASTExpressionList * constraints)
{
    ConstraintsDescription res;
    if (constraints)
        for (const auto & constraint : constraints->children)
            res.constraints.push_back(std::dynamic_pointer_cast<ASTConstraintDeclaration>(constraint->clone()));
    return res;
}


InterpreterCreateQuery::TableProperties InterpreterCreateQuery::setProperties(ASTCreateQuery & create) const
{
    TableProperties properties;
    TableStructureReadLockHolder as_storage_lock;

    if (create.columns_list)
    {
        if (create.columns_list->columns)
            properties.columns = getColumnsDescription(*create.columns_list->columns, context);

        if (create.columns_list->indices)
            for (const auto & index : create.columns_list->indices->children)
                properties.indices.indices.push_back(
                    std::dynamic_pointer_cast<ASTIndexDeclaration>(index->clone()));

        properties.constraints = getConstraintsDescription(create.columns_list->constraints);
    }
    else if (!create.as_table.empty())
    {
        String as_database_name = create.as_database.empty() ? context.getCurrentDatabase() : create.as_database;
        StoragePtr as_storage = context.getTable(as_database_name, create.as_table);

        /// as_storage->getColumns() and setEngine(...) must be called under structure lock of other_table for CREATE ... AS other_table.
        as_storage_lock = as_storage->lockStructureForShare(false, context.getCurrentQueryId());
        properties.columns = as_storage->getColumns();

        /// Secondary indices make sense only for MergeTree family of storage engines.
        /// We should not copy them for other storages.
        if (create.storage && endsWith(create.storage->engine->name, "MergeTree"))
            properties.indices = as_storage->getIndices();

        properties.constraints = as_storage->getConstraints();
    }
    else if (create.select)
    {
        Block as_select_sample = InterpreterSelectWithUnionQuery::getSampleBlock(create.select->clone(), context);
        properties.columns = ColumnsDescription(as_select_sample.getNamesAndTypesList());
    }
    else if (create.as_table_function)
        return {};
    else
        throw Exception("Incorrect CREATE query: required list of column descriptions or AS section or SELECT.", ErrorCodes::INCORRECT_QUERY);


    /// Even if query has list of columns, canonicalize it (unfold Nested columns).
    if (!create.columns_list)
        create.set(create.columns_list, std::make_shared<ASTColumns>());

    ASTPtr new_columns = formatColumns(properties.columns);
    ASTPtr new_indices = formatIndices(properties.indices);
    ASTPtr new_constraints = formatConstraints(properties.constraints);

    create.columns_list->setOrReplace(create.columns_list->columns, new_columns);
    create.columns_list->setOrReplace(create.columns_list->indices, new_indices);
    create.columns_list->setOrReplace(create.columns_list->constraints, new_constraints);

    validateTableStructure(create, properties);

    /// Set the table engine if it was not specified explicitly.
    setEngine(create);
    return properties;
}

void InterpreterCreateQuery::validateTableStructure(const ASTCreateQuery & create,
                                                    const InterpreterCreateQuery::TableProperties & properties) const
{
    /// Check for duplicates
    std::set<String> all_columns;
    for (const auto & column : properties.columns)
    {
        if (!all_columns.emplace(column.name).second)
            throw Exception("Column " + backQuoteIfNeed(column.name) + " already exists", ErrorCodes::DUPLICATE_COLUMN);
    }

    /// Check low cardinality types in creating table if it was not allowed in setting
    if (!create.attach && !context.getSettingsRef().allow_suspicious_low_cardinality_types && !create.is_materialized_view)
    {
        for (const auto & name_and_type_pair : properties.columns.getAllPhysical())
        {
            if (const auto * current_type_ptr = typeid_cast<const DataTypeLowCardinality *>(name_and_type_pair.type.get()))
            {
                if (!isStringOrFixedString(*removeNullable(current_type_ptr->getDictionaryType())))
                    throw Exception("Creating columns of type " + current_type_ptr->getName() + " is prohibited by default "
                                    "due to expected negative impact on performance. "
                                    "It can be enabled with the \"allow_suspicious_low_cardinality_types\" setting.",
                                    ErrorCodes::SUSPICIOUS_TYPE_FOR_LOW_CARDINALITY);
            }
        }
    }
}

void InterpreterCreateQuery::setEngine(ASTCreateQuery & create) const
{
    if (create.storage)
    {
        if (create.temporary && create.storage->engine->name != "Memory")
            throw Exception(
                "Temporary tables can only be created with ENGINE = Memory, not " + create.storage->engine->name,
                ErrorCodes::INCORRECT_QUERY);

        return;
    }

    if (create.temporary && !create.is_live_view)
    {
        auto engine_ast = std::make_shared<ASTFunction>();
        engine_ast->name = "Memory";
        auto storage_ast = std::make_shared<ASTStorage>();
        storage_ast->set(storage_ast->engine, engine_ast);
        create.set(create.storage, storage_ast);
    }
    else if (!create.as_table.empty())
    {
        /// NOTE Getting the structure from the table specified in the AS is done not atomically with the creation of the table.

        String as_database_name = create.as_database.empty() ? context.getCurrentDatabase() : create.as_database;
        String as_table_name = create.as_table;

        ASTPtr as_create_ptr = context.getCreateTableQuery(as_database_name, as_table_name);
        const auto & as_create = as_create_ptr->as<ASTCreateQuery &>();

        if (as_create.is_view)
            throw Exception(
                "Cannot CREATE a table AS " + as_database_name + "." + as_table_name + ", it is a View",
                ErrorCodes::INCORRECT_QUERY);

        if (as_create.is_live_view)
            throw Exception(
                "Cannot CREATE a table AS " + as_database_name + "." + as_table_name + ", it is a Live View",
                ErrorCodes::INCORRECT_QUERY);

        create.set(create.storage, as_create.storage->ptr());
    }
}


BlockIO InterpreterCreateQuery::createTable(ASTCreateQuery & create)
{
    if (!create.cluster.empty())
    {
        NameSet databases{create.database};
        if (!create.to_table.empty())
            databases.emplace(create.to_database);

        /// NOTE: if it's CREATE query and create.database is DatabaseAtomic, different UUIDs will be generated on all servers.
        /// However, it allows to use UUID as replica name.

        return executeDDLQueryOnCluster(query_ptr, context, std::move(databases));
    }

    /// Temporary tables are created out of databases.
    if (create.temporary && !create.database.empty() && !create.is_live_view)
        throw Exception("Temporary tables cannot be inside a database. You should not specify a database for a temporary table.",
            ErrorCodes::BAD_DATABASE_FOR_TEMPORARY_TABLE);

    auto & database_name = create.database;
    auto & table_name = create.table;

    // If this is a stub ATTACH query, read the query definition from the database
    if (create.attach && !create.storage && !create.columns_list)
    {
        // Table SQL definition is available even if the table is detached
        auto query = context.getCreateTableQuery(database_name, table_name);
        create = query->as<ASTCreateQuery &>(); // Copy the saved create query, but use ATTACH instead of CREATE
        create.attach = true;
    }

    String current_database = context.getCurrentDatabase();
    if (create.database.empty())
        create.database = current_database;
    if (create.to_database.empty())
        create.to_database = current_database;

    if (create.select && (create.is_view || create.is_materialized_view || create.is_live_view))
    {
        AddDefaultDatabaseVisitor visitor(current_database);
        visitor.visit(*create.select);
    }

    /// Set and retrieve list of columns, indices and constraints. Set table engine if needed. Rewrite query in canonical way.
    TableProperties properties = setProperties(create);

    /// Actually creates table
    bool created = doCreateTable(create, properties);
    if (!created)
        return {};

    return fillTableIfNeeded(create, database_name);
}

bool InterpreterCreateQuery::doCreateTable(/*const*/ ASTCreateQuery & create,
                                           const InterpreterCreateQuery::TableProperties & properties)
{
    std::unique_ptr<DDLGuard> guard;

    String data_path;
    DatabasePtr database;

    const String & database_name = create.database;
    const String & table_name = create.table;
    bool need_add_to_database = !create.temporary || create.is_live_view;
    if (need_add_to_database)
    {
        database = context.getDatabase(database_name);
        if (database->getEngineName() == "Atomic")
        {
            //TODO implement ATTACH FROM 'path/to/data': generate UUID and move table data to store/
            if (create.attach && create.uuid.empty())
                throw Exception("UUID must be specified in ATTACH TABLE query for Atomic database engine", ErrorCodes::INCORRECT_QUERY);
            if (!create.attach && create.uuid.empty())
                create.uuid = boost::uuids::to_string(boost::uuids::random_generator()());
        }
        else
        {
            if (!create.uuid.empty())
                throw Exception("Table UUID specified, but engine of database " + database_name + " is not Atomic", ErrorCodes::INCORRECT_QUERY);
        }

        if (!create.attach && create.uuid.empty() && database->getEngineName() == "Atomic")
            create.uuid = boost::uuids::to_string(boost::uuids::random_generator()());

        data_path = database->getDataPath(create);

        /** If the request specifies IF NOT EXISTS, we allow concurrent CREATE queries (which do nothing).
          * If table doesnt exist, one thread is creating table, while others wait in DDLGuard.
          */
        guard = context.getDDLGuard(database_name, table_name);

        if (!create.attach && !data_path.empty() && Poco::File(context.getPath() + data_path).exists())
            throw Exception("Directory for table data " + data_path + " already exists", ErrorCodes::TABLE_ALREADY_EXISTS);

        /// Table can be created before or it can be created concurrently in another thread, while we were waiting in DDLGuard.
        if (database->isTableExist(context, table_name))
        {
            /// TODO Check structure of table
            if (create.if_not_exists)
                return false;
            else if (create.replace_view)
            {
                /// when executing CREATE OR REPLACE VIEW, drop current existing view
                auto drop_ast = std::make_shared<ASTDropQuery>();
                drop_ast->database = database_name;
                drop_ast->table = table_name;
                drop_ast->no_ddl_lock = true;

                InterpreterDropQuery interpreter(drop_ast, context);
                interpreter.execute();
            }
            else
                throw Exception("Table " + database_name + "." + table_name + " already exists.", ErrorCodes::TABLE_ALREADY_EXISTS);
        }
    }
    else if (context.tryGetExternalTable(table_name) && create.if_not_exists)
         return false;

    StoragePtr res;
    if (create.as_table_function)
    {
        const auto & table_function = create.as_table_function->as<ASTFunction &>();
        const auto & factory = TableFunctionFactory::instance();
        res = factory.get(table_function.name, context)->execute(create.as_table_function, context, create.table);
    }
    else
    {
        res = StorageFactory::instance().get(create,
            data_path,
            context,
            context.getGlobalContext(),
            properties.columns,
            properties.constraints,
            false);
    }

    if (need_add_to_database)
        database->createTable(context, table_name, res, query_ptr);
    else
        context.getSessionContext().addExternalTable(table_name, res, query_ptr);

    /// We must call "startup" and "shutdown" while holding DDLGuard.
    /// Because otherwise method "shutdown" (from InterpreterDropQuery) can be called before startup
    /// (in case when table was created and instantly dropped before started up)
    ///
    /// Method "startup" may create background tasks and method "shutdown" will wait for them.
    /// But if "shutdown" is called before "startup", it will exit early, because there are no background tasks to wait.
    /// Then background task is created by "startup" method. And when destructor of a table object is called, background task is still active,
    /// and the task will use references to freed data.

    res->startup();
    return true;
}

BlockIO InterpreterCreateQuery::fillTableIfNeeded(const ASTCreateQuery & create, const String & database_name)
{
    /// If the query is a CREATE SELECT, insert the data into the table.
    if (create.select && !create.attach
        && !create.is_view && !create.is_live_view && (!create.is_materialized_view || create.is_populate))
    {
        auto insert = std::make_shared<ASTInsertQuery>();

        if (!create.temporary)
            insert->database = database_name;

        insert->table = create.table;
        insert->select = create.select->clone();

        if (create.temporary && !context.getSessionContext().hasQueryContext())
            context.getSessionContext().makeQueryContext();

        return InterpreterInsertQuery(insert,
            create.temporary ? context.getSessionContext() : context,
            context.getSettingsRef().insert_allow_materialized_columns).execute();
    }

    return {};
}

BlockIO InterpreterCreateQuery::createDictionary(ASTCreateQuery & create)
{
    String dictionary_name = create.table;

    String database_name = !create.database.empty() ? create.database : context.getCurrentDatabase();

    auto guard = context.getDDLGuard(database_name, dictionary_name);
    DatabasePtr database = context.getDatabase(database_name);

    if (database->isDictionaryExist(context, dictionary_name))
    {
        /// TODO Check structure of dictionary
        if (create.if_not_exists)
            return {};
        else
            throw Exception(
                "Dictionary " + database_name + "." + dictionary_name + " already exists.", ErrorCodes::DICTIONARY_ALREADY_EXISTS);
    }

    if (create.attach)
    {
        auto query = context.getCreateDictionaryQuery(database_name, dictionary_name);
        create = query->as<ASTCreateQuery &>();
        create.attach = true;
    }

    if (create.attach)
        database->attachDictionary(dictionary_name, context);
    else
        database->createDictionary(context, dictionary_name, query_ptr);

    return {};
}

BlockIO InterpreterCreateQuery::execute()
{
    auto & create = query_ptr->as<ASTCreateQuery &>();
    checkAccess(create);
    ASTQueryWithOutput::resetOutputASTIfExist(create);

    /// CREATE|ATTACH DATABASE
    if (!create.database.empty() && create.table.empty())
        return createDatabase(create);
    else if (!create.is_dictionary)
        return createTable(create);
    else
        return createDictionary(create);
}


void InterpreterCreateQuery::checkAccess(const ASTCreateQuery & create)
{
    /// Internal queries (initiated by the server itself) always have access to everything.
    if (internal)
        return;

    const Settings & settings = context.getSettingsRef();
    auto readonly = settings.readonly;
    auto allow_ddl = settings.allow_ddl;

    if (!readonly && allow_ddl)
        return;

    /// CREATE|ATTACH DATABASE
    if (!create.database.empty() && create.table.empty())
    {
        if (readonly)
            throw Exception("Cannot create database in readonly mode", ErrorCodes::READONLY);

        throw Exception("Cannot create database. DDL queries are prohibited for the user", ErrorCodes::QUERY_IS_PROHIBITED);
    }
    String object = "table";

    if (create.is_dictionary)
    {
        if (readonly)
            throw Exception("Cannot create dictionary in readonly mode", ErrorCodes::READONLY);
        object = "dictionary";
    }

    if (create.temporary && readonly >= 2)
        return;

    if (readonly)
        throw Exception("Cannot create table or dictionary in readonly mode", ErrorCodes::READONLY);

    throw Exception("Cannot create " + object + ". DDL queries are prohibited for the user", ErrorCodes::QUERY_IS_PROHIBITED);
}

}