ClickHouse/dbms/include/DB/Interpreters/InterpreterExistsQuery.h

#pragma once

#include <DB/Storages/IStorage.h>
#include <DB/Parsers/TablePropertiesQueriesASTs.h>
#include <DB/Interpreters/Context.h>
#include <DB/Interpreters/IInterpreter.h>
#include <DB/DataStreams/OneBlockInputStream.h>
#include <DB/DataStreams/BlockIO.h>
#include <DB/DataStreams/copyData.h>
#include <DB/DataTypes/DataTypesNumberFixed.h>


namespace DB
{


/** Проверить, существует ли таблица. Вернуть одну строку с одним столбцом result типа UInt8 со значением 0 или 1.
  */
class InterpreterExistsQuery : public IInterpreter
{
public:
	InterpreterExistsQuery(ASTPtr query_ptr_, Context & context_)
		: query_ptr(query_ptr_), context(context_) {}

	BlockIO execute() override
	{
		BlockIO res;
		res.in = executeImpl();
		res.in_sample = getSampleBlock();

		return res;
	}

private:
	ASTPtr query_ptr;
	Context context;

	Block getSampleBlock()
	{
		return {{ std::make_shared<ColumnConstUInt8>(1, 0), std::make_shared<DataTypeUInt8>(), "result" }};
	}

	BlockInputStreamPtr executeImpl()
	{
		const ASTExistsQuery & ast = typeid_cast<const ASTExistsQuery &>(*query_ptr);
		bool res = context.isTableExist(ast.database, ast.table);

		return std::make_shared<OneBlockInputStream>(Block{{
			std::make_shared<ColumnConstUInt8>(1, res),
			std::make_shared<DataTypeUInt8>(),
			"result" }});
	}
};


}