How to Recover Deleted Data from SQL Server?

This is the most asked question in SQL Forums. How to recover deleted data by mistake from SQL Server? Most DB Admins will answer: “No, there is no way. If you do not have a backup of the data you cannot retrieve the deleted records.”

In this article, we say “Yes, there is a way”. So let us start by creating this procedure:

CREATE PROCEDURE Recover_Deleted_Data_Proc
@SchemaName_n_TableName NVARCHAR(Max),
@Date_From datetime=’1900/01/01′,
@Date_To datetime =’9999/12/31′
as

DECLARE @RowLogContents VARBINARY(8000)
DECLARE @TransactionID NVARCHAR(Max)
DECLARE @AllocUnitID BIGINT
Declare @AllocUnitName NVARCHAR(Max)
Declare @SQL NVARCHAR(Max)
DECLARE @bitTable TABLE
(
[ID] INT,
[Bitvalue] INT
)

INSERT INTO @bitTable
SELECT 0,2 UNION ALL
SELECT 1,2 UNION ALL
SELECT 2,4 UNION ALL
SELECT 3,8 UNION ALL
SELECT 4,16 UNION ALL
SELECT 5,32 UNION ALL
SELECT 6,64 UNION ALL
SELECT 7,128

–Create table to collect the row data.

DECLARE @DeletedRecords TABLE
(
[RowLogContents] VARBINARY(8000),
[AllocUnitID] BIGINT,
[Transaction ID] NVARCHAR(Max),
[FixedLengthData] SMALLINT,
[TotalNoOfCols] SMALLINT,
[NullBitMapLength] SMALLINT,
[NullBytes] VARBINARY(8000),
[TotalNoofVarCols] SMALLINT,
[ColumnOffsetArray] VARBINARY(8000),
[VarColumnStart] SMALLINT,
[NullBitMap] VARCHAR(MAX)
)

–Create a common table expression to get all the row data plus how many bytes we have for each row.

;WITH RowData AS (
SELECT
[RowLog Contents 0] AS [RowLogContents]
,[AllocUnitID] AS [AllocUnitID]
,[Transaction ID] AS [Transaction ID]
,CONVERT(SMALLINT, CONVERT(BINARY(2), REVERSE(SUBSTRING([RowLog Contents 0], 2 + 1, 2)))) AS [FixedLengthData] –@FixedLengthData
,CONVERT(INT, CONVERT(BINARY(2), REVERSE(SUBSTRING([RowLog Contents 0], CONVERT(SMALLINT, CONVERT(BINARY(2)
,REVERSE(SUBSTRING([RowLog Contents 0], 2 + 1, 2)))) + 1, 2)))) as [TotalNoOfCols]
,CONVERT(INT, ceiling(CONVERT(INT, CONVERT(BINARY(2), REVERSE(SUBSTRING([RowLog Contents 0], CONVERT(SMALLINT, CONVERT(BINARY(2)
,REVERSE(SUBSTRING([RowLog Contents 0], 2 + 1, 2)))) + 1, 2))))/8.0)) as [NullBitMapLength]
,SUBSTRING([RowLog Contents 0], CONVERT(SMALLINT, CONVERT(BINARY(2), REVERSE(SUBSTRING([RowLog Contents 0], 2 + 1, 2)))) + 3,
CONVERT(INT, ceiling(CONVERT(INT, CONVERT(BINARY(2), REVERSE(SUBSTRING([RowLog Contents 0], CONVERT(SMALLINT, CONVERT(BINARY(2)
,REVERSE(SUBSTRING([RowLog Contents 0], 2 + 1, 2)))) + 1, 2))))/8.0))) as [NullBytes]
,(CASE WHEN SUBSTRING([RowLog Contents 0], 1, 1) In (0×30,0×70) THEN
CONVERT(INT, CONVERT(BINARY(2), REVERSE(SUBSTRING([RowLog Contents 0],
CONVERT(SMALLINT, CONVERT(BINARY(2), REVERSE(SUBSTRING([RowLog Contents 0], 2 + 1, 2)))) + 3
+ CONVERT(INT, ceiling(CONVERT(INT, CONVERT(BINARY(2), REVERSE(SUBSTRING([RowLog Contents 0], CONVERT(SMALLINT, CONVERT(BINARY(2)
,REVERSE(SUBSTRING([RowLog Contents 0], 2 + 1, 2)))) + 1, 2))))/8.0)), 2)))) ELSE null END) AS [TotalNoofVarCols]
,(CASE WHEN SUBSTRING([RowLog Contents 0], 1, 1) In (0×30,0×70) THEN
SUBSTRING([RowLog Contents 0]
, CONVERT(SMALLINT, CONVERT(BINARY(2), REVERSE(SUBSTRING([RowLog Contents 0], 2 + 1, 2)))) + 3
+ CONVERT(INT, ceiling(CONVERT(INT, CONVERT(BINARY(2), REVERSE(SUBSTRING([RowLog Contents 0], CONVERT(SMALLINT, CONVERT(BINARY(2)
,REVERSE(SUBSTRING([RowLog Contents 0], 2 + 1, 2)))) + 1, 2))))/8.0)) + 2
, (CASE WHEN SUBSTRING([RowLog Contents 0], 1, 1) In (0×30,0×70) THEN
CONVERT(INT, CONVERT(BINARY(2), REVERSE(SUBSTRING([RowLog Contents 0],
CONVERT(SMALLINT, CONVERT(BINARY(2), REVERSE(SUBSTRING([RowLog Contents 0], 2 + 1, 2)))) + 3
+ CONVERT(INT, ceiling(CONVERT(INT, CONVERT(BINARY(2), REVERSE(SUBSTRING([RowLog Contents 0], CONVERT(SMALLINT, CONVERT(BINARY(2)
,REVERSE(SUBSTRING([RowLog Contents 0], 2 + 1, 2)))) + 1, 2))))/8.0)), 2)))) ELSE null END)
* 2) ELSE null END) AS [ColumnOffsetArray]
,CASE WHEN SUBSTRING([RowLog Contents 0], 1, 1)In (0×30,0×70)
THEN (
CONVERT(SMALLINT, CONVERT(BINARY(2), REVERSE(SUBSTRING([RowLog Contents 0], 2 + 1, 2)))) + 4
+ CONVERT(INT, ceiling(CONVERT(INT, CONVERT(BINARY(2), REVERSE(SUBSTRING([RowLog Contents 0], CONVERT(SMALLINT, CONVERT(BINARY(2)
,REVERSE(SUBSTRING([RowLog Contents 0], 2 + 1, 2)))) + 1, 2))))/8.0))
+ ((CASE WHEN SUBSTRING([RowLog Contents 0], 1, 1) In (0×30,0×70) THEN
CONVERT(INT, CONVERT(BINARY(2), REVERSE(SUBSTRING([RowLog Contents 0],
CONVERT(SMALLINT, CONVERT(BINARY(2), REVERSE(SUBSTRING([RowLog Contents 0], 2 + 1, 2)))) + 3
+ CONVERT(INT, ceiling(CONVERT(INT, CONVERT(BINARY(2), REVERSE(SUBSTRING([RowLog Contents 0], CONVERT(SMALLINT, CONVERT(BINARY(2)
,REVERSE(SUBSTRING([RowLog Contents 0], 2 + 1, 2)))) + 1, 2))))/8.0)), 2)))) ELSE null END) * 2))
ELSE null End AS [VarColumnStart]
FROM sys.fn_dblog(NULL, NULL)
WHERE
AllocUnitId IN
(Select [Allocation_unit_id] from sys.allocation_units allocunits
INNER JOIN sys.partitions partitions ON (allocunits.type IN (1, 3)
AND partitions.hobt_id = allocunits.container_id) OR (allocunits.type = 2
AND partitions.partition_id = allocunits.container_id)
Where object_id=object_ID(” + @SchemaName_n_TableName + ”))
AND Context IN (‘LCX_MARK_AS_GHOST’, ‘LCX_HEAP’) AND Operation in (‘LOP_DELETE_ROWS’)
And SUBSTRING([RowLog Contents 0], 1, 1)In (0×30,0×70)
AND [TRANSACTION ID] IN (Select DISTINCT [TRANSACTION ID] FROM sys.fn_dblog(NULL, NULL)
Where Context IN (‘LCX_NULL’) AND Operation in (‘LOP_BEGIN_XACT’)
And [Transaction Name]=’DELETE’
And CONVERT(NVARCHAR(11),[Begin Time]) BETWEEN @Date_From AND @Date_To)),
N1 (n) AS (SELECT 1 UNION ALL SELECT 1),
N2 (n) AS (SELECT 1 FROM N1 AS X, N1 AS Y),
N3 (n) AS (SELECT 1 FROM N2 AS X, N2 AS Y),
N4 (n) AS (SELECT ROW_NUMBER() OVER(ORDER BY X.n)
FROM N3 AS X, N3 AS Y)
insert into @DeletedRecords
Select RowLogContents
,[AllocUnitID]
,[Transaction ID]
,[FixedLengthData]
,[TotalNoOfCols]
,[NullBitMapLength]
,[NullBytes]
,[TotalNoofVarCols]
,[ColumnOffsetArray]
,[VarColumnStart]
,[NullBitMap]=(REPLACE(STUFF((SELECT ‘,’ +
(CASE WHEN [ID]=0 THEN CONVERT(NVARCHAR(1),(SUBSTRING(NullBytes, n, 1) % 2)) ELSE CONVERT(NVARCHAR(1),((SUBSTRING(NullBytes, n, 1) / [Bitvalue]) % 2)) END) –as [nullBitMap]
FROM
N4 AS Nums
Join RowData AS C ON n<=NullBitMapLength
Cross Join @bitTable WHERE C.[RowLogContents]=D.[RowLogContents] ORDER BY [RowLogContents],n ASC FOR XML PATH(”)),1,1,”),’,',”))
FROM RowData D
CREATE TABLE [#temp_Data]
(
[FieldName] VARCHAR(MAX),
[FieldValue] VARCHAR(MAX),
[Rowlogcontents] VARBINARY(8000)
)
–Create common table expression and join it with the rowdata table
– to get each column details
;With CTE AS (

/*This part is for variable data columns*/

SELECT Rowlogcontents,
NAME ,
cols.leaf_null_bit AS nullbit,
leaf_offset,
ISNULL(syscolumns.length, cols.max_length) AS [length],
cols.system_type_id,
cols.leaf_bit_position AS bitpos,
ISNULL(syscolumns.xprec, cols.precision) AS xprec,
ISNULL(syscolumns.xscale, cols.scale) AS xscale,
SUBSTRING([nullBitMap], cols.leaf_null_bit, 1) AS is_null,
–Calculate the variable column size from the variable column offset array
(CASE WHEN leaf_offset<1 and SUBSTRING([nullBitMap], cols.leaf_null_bit, 1)=0 THEN
CONVERT(SMALLINT, CONVERT(BINARY(2), REVERSE (SUBSTRING ([ColumnOffsetArray], (2 * leaf_offset*-1) – 1, 2)))) ELSE 0 END) AS [Column value Size],
—Calculate the column length
(CASE WHEN leaf_offset<1 and SUBSTRING([nullBitMap], cols.leaf_null_bit, 1)=0 THEN CONVERT(SMALLINT, CONVERT(BINARY(2), REVERSE (SUBSTRING ([ColumnOffsetArray], (2 * (leaf_offset*-1)) – 1, 2))))
- ISNULL(NULLIF(CONVERT(SMALLINT, CONVERT(BINARY(2), REVERSE (SUBSTRING ([ColumnOffsetArray], (2 * ((leaf_offset*-1) – 1)) – 1, 2)))), 0), [varColumnStart])
ELSE 0 END) AS [Column Length]

–Get the Hexa decimal value from the RowlogContent
–HexValue of the variable column=Substring([Column value Size] – [Column Length] + 1,[Column Length])
–This is the data of your column but in the Hexvalue
,CASE WHEN SUBSTRING([nullBitMap], cols.leaf_null_bit, 1)=1 THEN NULL ELSE
SUBSTRING(Rowlogcontents,((CASE WHEN leaf_offset<1 and SUBSTRING([nullBitMap], cols.leaf_null_bit, 1)=0 THEN CONVERT(SMALLINT, CONVERT(BINARY(2), REVERSE (SUBSTRING ([ColumnOffsetArray], (2 * leaf_offset*-1) – 1, 2)))) ELSE 0 END)
- ((CASE WHEN leaf_offset<1 and SUBSTRING([nullBitMap], cols.leaf_null_bit, 1)=0 THEN CONVERT(SMALLINT, CONVERT(BINARY(2), REVERSE (SUBSTRING ([ColumnOffsetArray], (2 * (leaf_offset*-1)) – 1, 2))))
- ISNULL(NULLIF(CONVERT(SMALLINT, CONVERT(BINARY(2), REVERSE (SUBSTRING ([ColumnOffsetArray], (2 * ((leaf_offset*-1) – 1)) – 1, 2)))), 0), [varColumnStart])
ELSE 0 END))) + 1,((CASE WHEN leaf_offset<1 and SUBSTRING([nullBitMap], cols.leaf_null_bit, 1)=0 THEN CONVERT(SMALLINT, CONVERT(BINARY(2), REVERSE (SUBSTRING ([ColumnOffsetArray], (2 * (leaf_offset*-1)) – 1, 2))))
- ISNULL(NULLIF(CONVERT(SMALLINT, CONVERT(BINARY(2), REVERSE (SUBSTRING ([ColumnOffsetArray], (2 * ((leaf_offset*-1) – 1)) – 1, 2)))), 0), [varColumnStart])
ELSE 0 END))) END AS hex_Value

FROM @DeletedRecords A
Inner Join sys.allocation_units allocunits On A.[AllocUnitId]=allocunits.[Allocation_Unit_Id]
INNER JOIN sys.partitions partitions ON (allocunits.type IN (1, 3)
AND partitions.hobt_id = allocunits.container_id) OR (allocunits.type = 2 AND partitions.partition_id = allocunits.container_id)
INNER JOIN sys.system_internals_partition_columns cols ON cols.partition_id = partitions.partition_id
LEFT OUTER JOIN syscolumns ON syscolumns.id = partitions.object_id AND syscolumns.colid = cols.partition_column_id
WHERE leaf_offset<0

UNION

/*This part is for fixed data columns*/
SELECT Rowlogcontents,
NAME ,
cols.leaf_null_bit AS nullbit,
leaf_offset,
ISNULL(syscolumns.length, cols.max_length) AS [length],
cols.system_type_id,
cols.leaf_bit_position AS bitpos,
ISNULL(syscolumns.xprec, cols.precision) AS xprec,
ISNULL(syscolumns.xscale, cols.scale) AS xscale,
SUBSTRING([nullBitMap], cols.leaf_null_bit, 1) AS is_null,
(SELECT TOP 1 ISNULL(SUM(CASE WHEN C.leaf_offset >1 THEN max_length ELSE 0 END),0) FROM
sys.system_internals_partition_columns C WHERE cols.partition_id =C.partition_id And C.leaf_null_bit<cols.leaf_null_bit)+5 AS [Column value Size],
syscolumns.length AS [Column Length]
,CASE WHEN SUBSTRING([nullBitMap], cols.leaf_null_bit, 1)=1 THEN NULL ELSE
SUBSTRING
(
Rowlogcontents,(SELECT TOP 1 ISNULL(SUM(CASE WHEN C.leaf_offset >1 THEN max_length ELSE 0 END),0) FROM
sys.system_internals_partition_columns C where cols.partition_id =C.partition_id And C.leaf_null_bit<cols.leaf_null_bit)+5
,syscolumns.length) END AS hex_Value

FROM @DeletedRecords A
Inner Join sys.allocation_units allocunits ON A.[AllocUnitId]=allocunits.[Allocation_Unit_Id]
INNER JOIN sys.partitions partitions ON (allocunits.type IN (1, 3)
AND partitions.hobt_id = allocunits.container_id) OR (allocunits.type = 2 AND partitions.partition_id = allocunits.container_id)
INNER JOIN sys.system_internals_partition_columns cols ON cols.partition_id = partitions.partition_id
LEFT OUTER JOIN syscolumns ON syscolumns.id = partitions.object_id AND syscolumns.colid = cols.partition_column_id
WHERE leaf_offset>0 )

–Converting data from Hexvalue to its orgional datatype.
–Implemented datatype conversion mechanism for each datatype

INSERT INTO #temp_Data
SELECT NAME,
CASE
WHEN system_type_id IN (231, 239) THEN LTRIM(RTRIM(CONVERT(NVARCHAR(max),hex_Value))) –NVARCHAR ,NCHAR
WHEN system_type_id IN (167,175) THEN LTRIM(RTRIM(CONVERT(VARCHAR(max),REPLACE(hex_Value, 0×00, 0×20)))) –VARCHAR,CHAR
WHEN system_type_id = 48 THEN CONVERT(VARCHAR(MAX), CONVERT(TINYINT, CONVERT(BINARY(1), REVERSE (hex_Value)))) –TINY INTEGER
WHEN system_type_id = 52 THEN CONVERT(VARCHAR(MAX), CONVERT(SMALLINT, CONVERT(BINARY(2), REVERSE (hex_Value)))) –SMALL INTEGER
WHEN system_type_id = 56 THEN CONVERT(VARCHAR(MAX), CONVERT(INT, CONVERT(BINARY(4), REVERSE(hex_Value)))) — INTEGER
WHEN system_type_id = 127 THEN CONVERT(VARCHAR(MAX), CONVERT(BIGINT, CONVERT(BINARY(8), REVERSE(hex_Value))))– BIG INTEGER
WHEN system_type_id = 61 Then CONVERT(VARCHAR(MAX),CONVERT(DATETIME,CONVERT(VARBINARY(8000),REVERSE (hex_Value))),100) –DATETIME
WHEN system_type_id =58 Then CONVERT(VARCHAR(MAX),CONVERT(SMALLDATETIME,CONVERT(VARBINARY(8000),REVERSE(hex_Value))),100) –SMALL DATETIME
WHEN system_type_id = 108 THEN CONVERT(VARCHAR(MAX),CONVERT(NUMERIC(38,20), CONVERT(VARBINARY,CONVERT(VARBINARY(1),xprec)+CONVERT(VARBINARY(1),xscale))+CONVERT(VARBINARY(1),0) + hex_Value)) — NUMERIC
WHEN system_type_id In(60,122) THEN CONVERT(VARCHAR(MAX),Convert(MONEY,Convert(VARBINARY(8000),Reverse(hex_Value))),2) –MONEY,SMALLMONEY
WHEN system_type_id =106 THEN CONVERT(VARCHAR(MAX), CAST(CONVERT(Decimal(38,34), CONVERT(VARBINARY,Convert(VARBINARY,xprec)+CONVERT(VARBINARY,xscale))+CONVERT(VARBINARY(1),0) + hex_Value) as FLOAT)) — DECIMAL
WHEN system_type_id = 104 THEN CONVERT(VARCHAR(MAX),CONVERT (BIT,CONVERT(BINARY(1), hex_Value)%2)) — BIT
WHEN system_type_id =62 THEN RTRIM(LTRIM(STR(CONVERT(FLOAT,SIGN(CAST(CONVERT(VARBINARY(8000),Reverse(hex_Value)) AS BIGINT)) * (1.0 + (CAST(CONVERT(VARBINARY(8000),Reverse(hex_Value)) AS BIGINT) & 0x000FFFFFFFFFFFFF) * POWER(CAST(2 AS FLOAT), -52)) * POWER(CAST(2 AS FLOAT),((CAST(CONVERT(VARBINARY(8000),Reverse(hex_Value)) AS BIGINT) & 0x7ff0000000000000) / EXP(52 * LOG(2))-1023))),53,LEN(hex_Value)))) — FLOAT
When system_type_id =59 THEN Left(LTRIM(STR(CAST(SIGN(CAST(Convert(VARBINARY(8000),REVERSE(hex_Value)) AS BIGINT))* (1.0 + (CAST(CONVERT(VARBINARY(8000),Reverse(hex_Value)) AS BIGINT) & 0x007FFFFF) * POWER(CAST(2 AS Real), -23)) * POWER(CAST(2 AS Real),(((CAST(CONVERT(VARBINARY(8000),Reverse(hex_Value)) AS INT) )& 0x7f800000)/ EXP(23 * LOG(2))-127))AS REAL),23,23)),8) –Real
WHEN system_type_id In (165,173) THEN (CASE WHEN CHARINDEX(0x,cast(” AS XML).value(‘xs:hexBinary(sql:column(“hex_Value”))’, ‘VARBINARY(8000)’)) = 0 THEN ’0x’ ELSE ” END) +cast(” AS XML).value(‘xs:hexBinary(sql:column(“hex_Value”))’, ‘varchar(max)’) — BINARY,VARBINARY
WHEN system_type_id =36 THEN CONVERT(VARCHAR(MAX),CONVERT(UNIQUEIDENTIFIER,hex_Value)) –UNIQUEIDENTIFIER
END AS FieldValue
,[Rowlogcontents]
FROM CTE ORDER BY nullbit

–Create the column name in the same order to do pivot table.

DECLARE @FieldName VARCHAR(max)
SET @FieldName = STUFF(
(
SELECT ‘,’ + CAST(QUOTENAME([Name]) AS VARCHAR(MAX)) FROM syscolumns WHERE id=object_id(” + @SchemaName_n_TableName + ”)
FOR XML PATH(”)
), 1, 1, ”)

–Finally did pivot table and get the data back in the same format.
SET @sql = ‘SELECT ‘ + @FieldName + ‘ FROM #temp_Data PIVOT (Min([FieldValue]) FOR FieldName IN (‘ + @FieldName + ‘)) AS pvt’

EXEC sp_executesql @sql

GO

 

After creating this procedure, you can just call it with the table name as parameters and specify a date range to get the deleted records in a period.

EXEC Recover_Deleted_Data_Proc 'dbo.Employees'

It works like magic!