How To Recover Deleted Rows In SQL Server

Yashwant Vishwakarma
May 12, 2016
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Note - All screenshots are applied to SQL Server 2012 Enterprise Evaluation Edition.

Introduction

We can recover deleted rows if we know the time when data is deleted We can achieve this goal using LSN ( Log Sequence Numbers ). As per Microsoft, “Every record in the SQL Server transaction log is uniquely identified by a log sequence number (LSN)". We will use these LSNs to recover our deleted data.

Requirements

To recover deleted rows from the table in database, database must be FULL Recovery or BULK-LOGGED Recovery Model.

SIMPLE Recovery doesn’t support transaction logs backup hence it is not possible in SIMPLE recovery model.

Steps Involved

Let’s set up environment for recovering deleted rows step by step:

Step 1-

Create a database name RecoverDeletedData and set recovery model as FULL if it is not set as FULL.

Use the following command to create database,

USE Master
GO
CREATE DATABASE [RecoverDeletedData]
ON PRIMARY
( NAME = N'RecoverDeletedData',
FILENAME = N'D:\RecoverDeletedData\RecoverDeletedData.mdf'
SIZE = 4096KB, FILEGROWTH = 1024KB )
LOG ON
( NAME = N'RecoverDeletedData_log',
FILENAME = N'D:\RecoverDeletedData\RecoverDeletedData.ldf',
SIZE = 1024KB, FILEGROWTH = 10%)
GO

Figure 1 - Creating database RecoverDeletedData

Step 2-

In Step 2 we will create a table for our environment.

CREATE TABLE [Friends] (
[Sr.No] INT IDENTITY,
[Name] varchar (50),
[City] varchar (50));

Step 3-

After creating table “Friends”, let’s insert some values into it.

USE RecoverDeletedData
GO

insert into friends values (1, 'IanRox', 'Delhi')
insert into friends values (2, 'Jim', 'New York')
insert into friends values (3, 'Catherine', 'Las Vegas')
insert into friends values (4, 'John', 'California')
insert into friends values (5, 'Katie', 'Mexico')
insert into friends values (6, 'Sabrina', 'Indiana')
insert into friends values (7, 'Alfred', 'Hamburg')
insert into friends values (8, 'Vaibhav', 'Bangalore')
insert into friends values (9, 'Vijeta', 'Mumbai')
insert into friends values (10, 'YashRox', 'Sultanpur')

Step 4-

After inserting records check the inserted records with below query-

USE RecoverDeletedData
GO
Select * from friends

Figure 2 - Fetching data from friends table of RecoverDeletedData database

Step 5-

In Step 5, we will take full backup of database “RecoverDeletedData”

USE RecoverDeletedData
GO
BACKUP DATABASE [RecoverDeletedData]
TO DISK = N'D:\RecoverDeletedData\RDDFull.bak'
WITH NOFORMAT, NOINIT, NAME = N'RecoverDeletedData-Full Database Backup',
SKIP, NOREWIND, NOUNLOAD, STATS = 10
GO

Figure 3 - Full Backup database RecoverDeletedData

Step 6-

Now we will go ahead and delete some rows so that we can recover them with the help of LSNs.

USE RecoverDeletedData
GO
DELETE friends
[WHERE [Sr.No] >5
GO

Figure 4 - Deleting rows from friends table

Step 7-

Now check the “friends” again from below query:

select * from friends

Figure 5 - Fetching rows from friends table after deletion

Ah! Only 5 records left as we deleted the records from 6th rows to 10th rows.

Step 8-

Now take transaction log backup of the database.

USE RecoverDeletedData

GO
BACKUP LOG [RecoverDeletedData]
TO DISK = N'D:\RecoverDeletedData\RDDTrLog.trn'
WITH NOFORMAT, NOINIT,
NAME = N'RecoverDeletedData-Transaction Log Backup',
SKIP, NOREWIND, NOUNLOAD, STATS = 10
GO

Figure 6 - Backup transaction log for RecoverDeletedData

Step 9-

Now to recover deleted rows we must gather information for deleted rows. To gather information about deleted rows we can run below query-

USE RecoverDeletedData
GO
Select [Current LSN] LSN], [Transaction ID], Operation, Context, AllocUnitName
FROM
fn_dblog(NULL, NULL)
WHERE Operation = 'LOP_DELETE_ROWS'

Figure 7 - Finding Transaction ID of deleted rows

From the above query we will get Transaction ID of deleted rows, now we have to find at what time rows got deleted.

Step 10-

In Step 10, we will find exact time when rows got deleted with below query using Transaction ID “000:000002f1”:

USE RecoverDeletedData
GO

SELECT
[Current LSN], Operation, [Transaction ID], [Begin Time], [Transaction Name], [Transaction SID]
FROM
fn_dblog(NULL, NULL)
WHERE
[Transaction ID] = ‘000:000002f1'
AND
[Operation] = 'LOP_BEGIN_XACT'

After executing the above query we will get the current LSN “00000025:000001d0:0001” [Apology, here I forgot to take screenshot]

Step 11-

In Step 11, we will proceed with restore operation to recover deleted rows with below query:

USE RecoverDeletedData
GO

RESTORE DATABASE RecoverDeletedData_COPY FROM
DISK = 'D:\RecoverDeletedData\RDDFull.bak'
WITH
MOVE 'RecoverDeletedData' TO 'D:\RecoverDB\RecoverDeletedData.mdf',
MOVE 'RecoverDeletedData_log' TO 'D:\RecoverDB\RecoverDeletedData_log.ldf',
REPLACE, NORECOVERY;
GO

Figure 8 - Restoring with FULL backup

Step 12-

In Step 12, we will apply transaction log to restore deleted rows using LSN “00000025:000001d0:0001”

USE RecoverDeletedData
GO
RESTORE LOG RecoverDeletedData_COPY FROM DISK = N'D:\RecoverDeletedData\RDOTrLog.trn' WITH STOPBEFOREMARK = ‘lsn:0x00000025:000001d0:0001'

Figure 9 - Restoring transaction log using LSN

Here one thing we need to remember that the LSN values are in hexadecimal form and for restoring with LSN value we need it in decimal form. To convert it to decimal form just put 0x before LSN like below in stopbeforemark clause

STOPBEFOREMARK = ‘lsn:0x00000025:000001d0:0001'

Step 13-

As in above screenshot restore operation successfully completed, so here we check that our deleted records are back in RecoverDeletedData_Copy Database:

USE RecoverDeletedData_Copy
GO
Select * from friends

Figure 10 - Fetching records from RecoverDeletedData_Copy database

Wow!! We got all records back…

In this way we can recover deleted records for any database provided database is in FULL or BULK-LOGGED Recovery model.

Final Words

So from the above explanation and steps it is very clear that how we can recover deleted rows if we deleted it accidentally. But before that we must have idea about LSNs, transaction logs etc.