HOW RESTORE WITHOUT OVERWRITE EXISTING DATABASE ???????

Question

I create a test database named TESTONE
USE MASTER
GO
if DB_ID('testone') IS NOT null
drop database TESTONE
GO
CREATE DATABASE TESTONE
GO
and change recovery model to simple
alter database TESTONE set recovery simple
GO
so I create a sample table
use TESTONE
GO
create table table1(
id int identity primary key,
descr varchar(10)
go
I take a full backup of that database
USE master
GO
BACKUP DATABASE TESTONE
TO DISK=N'c:\TEMP\testone.bak'
WITH NOFORMAT, INIT, NAME = N'TESTONE', SKIP, NOREWIND, NOUNLOAD, STATS = 10
GO
after that i do something bad :-)
USE TESTONE
GO
drop table table1
go
USE master
GO
USE [master]
RESTORE DATABASE [TESTONE] FROM DISK = N'C:\TEMP\testone.bak' WITH RECOVERY, FILE = 1, NOUNLOAD, STATS = 5
GO
the restore command doesn't contains  WITH REPLACE clause and ....
if you expand the tables tree you'll find your deleted table
the database has been overwritten
Why?

Answer 1

That is the default behavior or RESTORE. Since you are restoring the same DB (not a different DB) and the DB is in simple recovery mode, it will overwrite the existing DB. See https://msdn.microsoft.com/en-us/library/ms186858.aspx.
Here is an excerpt from this link:
REPLACE Option Impact
REPLACE should be used rarely and only after careful consideration. Restore normally prevents accidentally overwriting a database with a different database. If the database specified in a RESTORE statement already exists on the current server and the specified
database family GUID differs from the database family GUID recorded in the backup set, the database is not restored. This is an important safeguard.
The REPLACE option overrides several important safety checks that restore normally performs. The overridden checks are as follows:
Restoring over an existing database with a backup taken of another database.
With the REPLACE option, restore allows you to overwrite an existing database with whatever database is in the backup set, even if the specified database name differs from the database name recorded in the backup set. This can result in accidentally overwriting
a database by a different database.
Restoring over a database using the full or bulk-logged recovery model where a tail-log backup has not been taken and the STOPAT option is not used.
With the REPLACE option, you can lose committed work, because the log written most recently has not been backed up.
Overwriting existing files.
For example, a mistake could allow overwriting files of the wrong type, such as .xls files, or that are being used by another database that is not online. Arbitrary data loss is possible if existing files are overwritten, although the restored database is complete.
Satish Kartan www.sqlfood.com