ClickHouse/dbms/src/Storages/StorageSystemTables.cpp

#include <DB/Columns/ColumnString.h>
#include <DB/DataTypes/DataTypeString.h>
#include <DB/DataStreams/OneBlockInputStream.h>
#include <DB/Storages/StorageSystemTables.h>
#include <DB/Common/VirtualColumnUtils.h>


namespace DB
{


StorageSystemTables::StorageSystemTables(const std::string & name_)
	: name(name_),
	columns
	{
		{"database", 	new DataTypeString},
		{"name", 		new DataTypeString},
		{"engine", 		new DataTypeString},
	}
{
}

StoragePtr StorageSystemTables::create(const std::string & name_)
{
	return (new StorageSystemTables(name_))->thisPtr();
}


static ColumnWithTypeAndName getFilteredDatabases(ASTPtr query, const Context & context)
{
	ColumnWithTypeAndName column;
	column.name = "database";
	column.type = new DataTypeString;
	column.column = new ColumnString;

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

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

	return block.getByPosition(0);
}


BlockInputStreams StorageSystemTables::read(
	const Names & column_names,
	ASTPtr query,
	const Context & context,
	const Settings & settings,
	QueryProcessingStage::Enum & processed_stage,
	const size_t max_block_size,
	const unsigned threads)
{
	check(column_names);
	processed_stage = QueryProcessingStage::FetchColumns;

	Block block;

	ColumnWithTypeAndName col_db;
	col_db.name = "database";
	col_db.type = new DataTypeString;
	col_db.column = new ColumnString;
	block.insert(col_db);

	ColumnWithTypeAndName col_name;
	col_name.name = "name";
	col_name.type = new DataTypeString;
	col_name.column = new ColumnString;
	block.insert(col_name);

	ColumnWithTypeAndName col_engine;
	col_engine.name = "engine";
	col_engine.type = new DataTypeString;
	col_engine.column = new ColumnString;
	block.insert(col_engine);

	Poco::ScopedLock<Poco::Mutex> lock(context.getMutex());

	ColumnWithTypeAndName filtered_databases_column = getFilteredDatabases(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_it = context.getDatabases().find(database_name);

		if (database_it == context.getDatabases().end())
			throw DB::Exception(std::string("Fail to find database " + database_name), DB::ErrorCodes::LOGICAL_ERROR);

		for (Tables::const_iterator jt = database_it->second.begin(); jt != database_it->second.end(); ++jt)
		{
			col_db.column->insert(database_name);
			col_name.column->insert(jt->first);
			col_engine.column->insert(jt->second->getName());
		}
	}

	return BlockInputStreams(1, new OneBlockInputStream(block));
}

}