bool ParserAliasImpl<ParserIdentifier>::parseImpl(Pos & pos, Pos end, ASTPtr & node, Pos & max_parsed_pos, Expected & expected)
{
	ParserWhiteSpaceOrComments ws;
	ParserString s_as("AS", true, true);
	ParserIdentifier id_p;

	bool has_as_word = s_as.parse(pos, end, node, max_parsed_pos, expected);
	if (!allow_alias_without_as_keyword && !has_as_word)
		return false;

	ws.ignore(pos, end);

	if (!id_p.parse(pos, end, node, max_parsed_pos, expected))
		return false;

	if (!has_as_word)
	{
		/** В этом случае алиас не может совпадать с ключевым словом - для того,
		  *  чтобы в запросе "SELECT x FROM t", слово FROM не считалось алиасом,
		  *  а в запросе "SELECT x FRO FROM t", слово FRO считалось алиасом.
		  */

		const String & name = static_cast<const ASTIdentifier &>(*node.get()).name;

		for (const char ** keyword = restricted_keywords; *keyword != nullptr; ++keyword)
			if (0 == strcasecmp(name.data(), *keyword))
				return false;
	}

	return true;
}
bool ParserCreateQuery::parseImpl(Pos & pos, ASTPtr & node, Expected & expected)
{
    ParserKeyword s_create("CREATE");
    ParserKeyword s_temporary("TEMPORARY");
    ParserKeyword s_attach("ATTACH");
    ParserKeyword s_table("TABLE");
    ParserKeyword s_database("DATABASE");
    ParserKeyword s_if_not_exists("IF NOT EXISTS");
    ParserKeyword s_as("AS");
    ParserKeyword s_view("VIEW");
    ParserKeyword s_materialized("MATERIALIZED");
    ParserKeyword s_populate("POPULATE");
    ParserToken s_dot(TokenType::Dot);
    ParserToken s_lparen(TokenType::OpeningRoundBracket);
    ParserToken s_rparen(TokenType::ClosingRoundBracket);
    ParserStorage storage_p;
    ParserIdentifier name_p;
    ParserColumnsOrIndicesDeclarationList columns_or_indices_p;
    ParserSelectWithUnionQuery select_p;

    ASTPtr database;
    ASTPtr table;
    ASTPtr columns_list;
    ASTPtr to_database;
    ASTPtr to_table;
    ASTPtr storage;
    ASTPtr as_database;
    ASTPtr as_table;
    ASTPtr select;
    String cluster_str;
    bool attach = false;
    bool if_not_exists = false;
    bool is_view = false;
    bool is_materialized_view = false;
    bool is_populate = false;
    bool is_temporary = false;

    if (!s_create.ignore(pos, expected))
    {
        if (s_attach.ignore(pos, expected))
            attach = true;
        else
            return false;
    }

    if (s_temporary.ignore(pos, expected))
    {
        is_temporary = true;
    }

    if (s_table.ignore(pos, expected))
    {
        if (s_if_not_exists.ignore(pos, expected))
            if_not_exists = true;

        if (!name_p.parse(pos, table, expected))
            return false;

        if (s_dot.ignore(pos, expected))
        {
            database = table;
            if (!name_p.parse(pos, table, expected))
                return false;
        }

        if (ParserKeyword{"ON"}.ignore(pos, expected))
        {
            if (!ASTQueryWithOnCluster::parse(pos, cluster_str, expected))
                return false;
        }

        // Shortcut for ATTACH a previously detached table
        if (attach && (!pos.isValid() || pos.get().type == TokenType::Semicolon))
        {
            auto query = std::make_shared<ASTCreateQuery>();
            node = query;

            query->attach = attach;
            query->if_not_exists = if_not_exists;
            query->cluster = cluster_str;

            getIdentifierName(database, query->database);
            getIdentifierName(table, query->table);

            return true;
        }

        /// List of columns.
        if (s_lparen.ignore(pos, expected))
        {
            if (!columns_or_indices_p.parse(pos, columns_list, expected))
                return false;

            if (!s_rparen.ignore(pos, expected))
                return false;

            if (!storage_p.parse(pos, storage, expected) && !is_temporary)
                return false;
        }
        else
        {
            storage_p.parse(pos, storage, expected);

            if (!s_as.ignore(pos, expected))
                return false;

            if (!select_p.parse(pos, select, expected)) /// AS SELECT ...
            {
                /// AS [db.]table
                if (!name_p.parse(pos, as_table, expected))
                    return false;

                if (s_dot.ignore(pos, expected))
                {
                    as_database = as_table;
                    if (!name_p.parse(pos, as_table, expected))
                        return false;
                }

                /// Optional - ENGINE can be specified.
                if (!storage)
                    storage_p.parse(pos, storage, expected);
            }
        }
    }
    else if (is_temporary)
        return false;
    else if (s_database.ignore(pos, expected))
    {
        if (s_if_not_exists.ignore(pos, expected))
            if_not_exists = true;

        if (!name_p.parse(pos, database, expected))
            return false;

        if (ParserKeyword{"ON"}.ignore(pos, expected))
        {
            if (!ASTQueryWithOnCluster::parse(pos, cluster_str, expected))
                return false;
        }

        storage_p.parse(pos, storage, expected);
    }
    else
    {
        /// VIEW or MATERIALIZED VIEW
        if (s_materialized.ignore(pos, expected))
        {
            is_materialized_view = true;
        }
        else
            is_view = true;

        if (!s_view.ignore(pos, expected))
            return false;

        if (s_if_not_exists.ignore(pos, expected))
            if_not_exists = true;

        if (!name_p.parse(pos, table, expected))
            return false;

        if (s_dot.ignore(pos, expected))
        {
            database = table;
            if (!name_p.parse(pos, table, expected))
                return false;
        }

        if (ParserKeyword{"ON"}.ignore(pos, expected))
        {
            if (!ASTQueryWithOnCluster::parse(pos, cluster_str, expected))
                return false;
        }

        // TO [db.]table
        if (ParserKeyword{"TO"}.ignore(pos, expected))
        {
            if (!name_p.parse(pos, to_table, expected))
                return false;

            if (s_dot.ignore(pos, expected))
            {
                to_database = to_table;
                if (!name_p.parse(pos, to_table, expected))
                    return false;
            }
        }

        /// Optional - a list of columns can be specified. It must fully comply with SELECT.
        if (s_lparen.ignore(pos, expected))
        {
            if (!columns_or_indices_p.parse(pos, columns_list, expected))
                return false;

            if (!s_rparen.ignore(pos, expected))
                return false;
        }

        if (is_materialized_view && !to_table)
        {
            /// Internal ENGINE for MATERIALIZED VIEW must be specified.
            if (!storage_p.parse(pos, storage, expected))
                return false;

            if (s_populate.ignore(pos, expected))
                is_populate = true;
        }

        /// AS SELECT ...
        if (!s_as.ignore(pos, expected))
            return false;

        if (!select_p.parse(pos, select, expected))
            return false;
    }

    auto query = std::make_shared<ASTCreateQuery>();
    node = query;

    query->attach = attach;
    query->if_not_exists = if_not_exists;
    query->is_view = is_view;
    query->is_materialized_view = is_materialized_view;
    query->is_populate = is_populate;
    query->temporary = is_temporary;

    getIdentifierName(database, query->database);
    getIdentifierName(table, query->table);
    query->cluster = cluster_str;

    getIdentifierName(to_database, query->to_database);
    getIdentifierName(to_table, query->to_table);

    query->set(query->columns_list, columns_list);
    query->set(query->storage, storage);

    getIdentifierName(as_database, query->as_database);
    getIdentifierName(as_table, query->as_table);
    query->set(query->select, select);

    return true;
}