ClickHouse/src/TableFunctions/TableFunctionMerge.cpp

#include <Common/OptimizedRegularExpression.h>
#include <Common/typeid_cast.h>
#include <Storages/StorageMerge.h>
#include <Parsers/ASTLiteral.h>
#include <Parsers/ASTFunction.h>
#include <TableFunctions/ITableFunction.h>
#include <Interpreters/evaluateConstantExpression.h>
#include <Interpreters/Context.h>
#include <Access/ContextAccess.h>
#include <TableFunctions/TableFunctionMerge.h>
#include <TableFunctions/TableFunctionFactory.h>
#include <TableFunctions/registerTableFunctions.h>


namespace DB
{

namespace ErrorCodes
{
    extern const int NUMBER_OF_ARGUMENTS_DOESNT_MATCH;
    extern const int UNKNOWN_TABLE;
}

namespace
{
    [[noreturn]] void throwNoTablesMatchRegexp(const String & source_database_regexp, const String & source_table_regexp)
    {
        throw Exception(
            "Error while executing table function merge. Neither no one database matches regular expression " + source_database_regexp
                + " nor in database matches " + source_database_regexp + " no one table matches regular expression: " + source_table_regexp,
            ErrorCodes::UNKNOWN_TABLE);
    }
}


void TableFunctionMerge::parseArguments(const ASTPtr & ast_function, ContextPtr context)
{
    ASTs & args_func = ast_function->children;

    if (args_func.size() != 1)
        throw Exception("Table function 'merge' requires exactly 2 arguments"
            " - name of source database and regexp for table names.",
            ErrorCodes::NUMBER_OF_ARGUMENTS_DOESNT_MATCH);

    ASTs & args = args_func.at(0)->children;

    if (args.size() != 2)
        throw Exception("Table function 'merge' requires exactly 2 arguments"
            " - name of source database and regexp for table names.",
            ErrorCodes::NUMBER_OF_ARGUMENTS_DOESNT_MATCH);

    auto [is_regexp, database_ast] = evaluateDatabaseNameForMergeEngine(args[0], context);

    database_is_regexp = is_regexp;

    if (!is_regexp)
        args[0] = database_ast;
    source_database_name_or_regexp = database_ast->as<ASTLiteral &>().value.safeGet<String>();

    args[1] = evaluateConstantExpressionAsLiteral(args[1], context);
    source_table_regexp = args[1]->as<ASTLiteral &>().value.safeGet<String>();
}


const std::unordered_map<String, std::unordered_set<String>> & TableFunctionMerge::getSourceDatabasesAndTables(ContextPtr context) const
{
    if (source_databases_and_tables)
        return *source_databases_and_tables;

    source_databases_and_tables.emplace();

    /// database_name is not a regexp
    if (!database_is_regexp)
    {
        auto source_tables = getMatchedTablesWithAccess(source_database_name_or_regexp, source_table_regexp, context);
        if (source_tables.empty())
            throwNoTablesMatchRegexp(source_database_name_or_regexp, source_table_regexp);
        (*source_databases_and_tables)[source_database_name_or_regexp] = source_tables;
    }

    /// database_name is a regexp
    else
    {
        OptimizedRegularExpression database_re(source_database_name_or_regexp);
        auto databases = DatabaseCatalog::instance().getDatabases();

        for (const auto & db : databases)
        {
            if (database_re.match(db.first))
            {
                auto source_tables = getMatchedTablesWithAccess(db.first, source_table_regexp, context);

                if (!source_tables.empty())
                    (*source_databases_and_tables)[db.first] = source_tables;
            }
        }

        if ((*source_databases_and_tables).empty())
            throwNoTablesMatchRegexp(source_database_name_or_regexp, source_table_regexp);
    }

    return *source_databases_and_tables;
}

ColumnsDescription TableFunctionMerge::getActualTableStructure(ContextPtr context) const
{
    for (const auto & db_with_tables : getSourceDatabasesAndTables(context))
    {
        auto storage = DatabaseCatalog::instance().tryGetTable(StorageID{db_with_tables.first, *db_with_tables.second.begin()}, context);
        if (storage)
            return ColumnsDescription{storage->getInMemoryMetadataPtr()->getColumns().getAllPhysical()};
    }

    throwNoTablesMatchRegexp(source_database_name_or_regexp, source_table_regexp);
}


StoragePtr TableFunctionMerge::executeImpl(const ASTPtr & /*ast_function*/, ContextPtr context, const std::string & table_name, ColumnsDescription /*cached_columns*/) const
{
    auto res = StorageMerge::create(
        StorageID(getDatabaseName(), table_name),
        getActualTableStructure(context),
        String{},
        source_database_name_or_regexp,
        database_is_regexp,
        getSourceDatabasesAndTables(context),
        context);

    res->startup();
    return res;
}

NameSet
TableFunctionMerge::getMatchedTablesWithAccess(const String & database_name, const String & table_regexp, const ContextPtr & context)
{
    OptimizedRegularExpression table_re(table_regexp);

    auto table_name_match = [&](const String & table_name) { return table_re.match(table_name); };

    auto access = context->getAccess();

    auto database = DatabaseCatalog::instance().getDatabase(database_name);

    bool granted_show_on_all_tables = access->isGranted(AccessType::SHOW_TABLES, database_name);
    bool granted_select_on_all_tables = access->isGranted(AccessType::SELECT, database_name);

    NameSet tables;

    for (auto it = database->getTablesIterator(context, table_name_match); it->isValid(); it->next())
    {
        if (!it->table())
            continue;
        bool granted_show = granted_show_on_all_tables || access->isGranted(AccessType::SHOW_TABLES, database_name, it->name());
        if (!granted_show)
            continue;
        if (!granted_select_on_all_tables)
            access->checkAccess(AccessType::SELECT, database_name, it->name());
        tables.insert(it->name());
    }
    return tables;
}

void registerTableFunctionMerge(TableFunctionFactory & factory)
{
    factory.registerFunction<TableFunctionMerge>();
}

}