ClickHouse/dbms/src/Storages/StorageNull.h

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#pragma once
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#include <ext/shared_ptr_helper.h>
#include <Core/NamesAndTypes.h>
#include <Storages/IStorage.h>
#include <DataStreams/NullBlockInputStream.h>
#include <DataStreams/NullBlockOutputStream.h>
namespace DB
{
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/** When writing, does nothing.
* When reading, returns nothing.
*/
class StorageNull : public ext::shared_ptr_helper<StorageNull>, public IStorage
{
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friend struct ext::shared_ptr_helper<StorageNull>;
public:
std::string getName() const override { return "Null"; }
std::string getTableName() const override { return table_name; }
std::string getDatabaseName() const override { return database_name; }
BlockInputStreams read(
const Names & column_names,
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const SelectQueryInfo &,
const Context & /*context*/,
QueryProcessingStage::Enum /*processing_stage*/,
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size_t,
unsigned) override
{
return { std::make_shared<NullBlockInputStream>(getSampleBlockForColumns(column_names)) };
}
BlockOutputStreamPtr write(const ASTPtr &, const Context &) override
{
return std::make_shared<NullBlockOutputStream>(getSampleBlock());
}
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void rename(const String & /*new_path_to_db*/, const String & new_database_name, const String & new_table_name, TableStructureWriteLockHolder &) override
{
table_name = new_table_name;
database_name = new_database_name;
}
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void alter(
const AlterCommands & params, const Context & context, TableStructureWriteLockHolder & table_lock_holder) override;
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private:
String table_name;
String database_name;
protected:
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StorageNull(String database_name_, String table_name_, ColumnsDescription columns_description_, ConstraintsDescription constraints_)
: table_name(std::move(table_name_)), database_name(std::move(database_name_))
{
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setColumns(std::move(columns_description_));
setConstraints(std::move(constraints_));
}
};
}