ClickHouse/dbms/include/DB/Interpreters/ClusterProxy/Query.h

#pragma once

#include <DB/Parsers/IAST.h>
#include <DB/Storages/IStorage.h>

namespace DB
{

struct Settings;
class Context;
class Cluster;

namespace ClusterProxy
{

class IQueryConstructor;

/// This class is designed for distributed queries execution. It hides from
/// the caller the details about the actual locations at which a distributed
/// query is performed. Depending on the type of query to be performed,
/// (currently SELECT, DESCRIBE, or ALTER (for resharding)), a so-called
/// query constructor is specified. Such an object states, among other things,
/// how connections must be allocated for remote execution.
class Query
{
public:
	Query(IQueryConstructor & query_constructor_, const Cluster & cluster_,
		ASTPtr query_ast_, const Context & context_, const Settings & settings_, bool enable_shard_multiplexing_);

	/// For each location at which we perform the query, create an input stream
	/// from which we can fetch the result.
	BlockInputStreams execute();

private:
	IQueryConstructor & query_constructor;
	const Cluster & cluster;
	ASTPtr query_ast;
	const Context & context;
	const Settings & settings;
	bool enable_shard_multiplexing;
};

}

}