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#pragma once
#include <Core/NamesAndTypes.h>
#include <Storages/IStorage.h>
#include <Processors/Sources/NullSource.h>
#include <Processors/Sinks/SinkToStorage.h>
#include <QueryPipeline/Pipe.h>
namespace DB
{
/** When writing, does nothing.
* When reading, returns nothing.
*/
class StorageNull final : public IStorage
{
public:
StorageNull(
const StorageID & table_id_, ColumnsDescription columns_description_, ConstraintsDescription constraints_, const String & comment)
: IStorage(table_id_)
{
StorageInMemoryMetadata storage_metadata;
storage_metadata.setColumns(columns_description_);
storage_metadata.setConstraints(constraints_);
storage_metadata.setComment(comment);
setInMemoryMetadata(storage_metadata);
}
std::string getName() const override { return "Null"; }
Pipe read(
const Names & column_names,
const StorageSnapshotPtr & storage_snapshot,
SelectQueryInfo &,
ContextPtr /*context*/,
QueryProcessingStage::Enum /*processing_stage*/,
size_t /*max_block_size*/,
size_t /*num_streams*/) override
{
return Pipe(
std::make_shared<NullSource>(storage_snapshot->getSampleBlockForColumns(column_names)));
}
bool parallelizeOutputAfterReading(ContextPtr) const override { return false; }
bool supportsParallelInsert() const override { return true; }
SinkToStoragePtr write(const ASTPtr &, const StorageMetadataPtr & metadata_snapshot, ContextPtr, bool) override
{
return std::make_shared<NullSinkToStorage>(metadata_snapshot->getSampleBlock());
}
void checkAlterIsPossible(const AlterCommands & commands, ContextPtr context) const override;
void alter(const AlterCommands & params, ContextPtr context, AlterLockHolder & table_lock_holder) override;
std::optional<UInt64> totalRows(const Settings &) const override
{
return {0};
}
std::optional<UInt64> totalBytes(const Settings &) const override
{
return {0};
}
};
}
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