Data Obfuscation

Question

Hi,

Running SQL Server 2017. I am working on an obfuscation process for production data. I have the following sample query:

UPDATE
[T1]
SET
[T1].[First_Name] = [S1].[First_Name],
[T1].[Last_Name] = [S1].[Last_Name],
FROM
(
SELECT
[Row_ID],
[First_Name],
[Last_Name]
FROM
[dbo].[Test]
) [T1]
CROSS APPLY
(
SELECT TOP 1
*
FROM
[dbo].[Sample]
WHERE
[T1].[Row_ID] = [T1].[Row_ID]
ORDER BY
NEWID() ASC
) [S1]

The first & last name combinations in the sample table are unique. At first glance the above query does the trick but on examination the same sample row is used more than once in the update. As my sample table has more rows than the production table, how can I ensure that a sample row is not used more than once in the update query?

Thanks!

Answer 1

Try the function in the below post if that helps you.

https://sqlzealots.com/2019/10/08/generate-random-character-in-sql-server/

Answer 2

Hi @VDT-7677 ,

For this type of problem we recommend that you post CREATE TABLE statements for your tables together with INSERT statements with sample data, enough to illustrate all angles of the problem. We also need to see the expected result of the sample.

You could try with below which has the least modification based on your code.

UPDATE [T1]  
SET  
[T1].[First_Name] = [S1].[First_Name],  
[T1].[Last_Name] = [S1].[Last_Name]  
FROM [dbo].[Test] [T1]  
CROSS APPLY  
(  
SELECT top 1 [First_Name],[Last_Name]  
FROM  
[dbo].[Sample]   
 --TABLESAMPLE (1000 ROWS) --add this line if necessary  
WHERE  
[T1].[Row_ID] = [T1].[Row_ID]  
ORDER BY  NEWID(),[T1].[Row_ID]  
) [S1]  

In additon, you could also try with Rank() function which is similar with RowNumber() function mentioned by Erland as below:

 ; WITH T1_numbering AS (  
     SELECT First_Name, Last_Name, RANK() OVER(ORDER BY Row_ID) AS RANKID  
     FROM   test  
 ), S_Numbering AS (  
    SELECT First_Name, Last_Name, RANK() OVER(ORDER BY newid()) AS RANKID  
    FROM   Sample  
 )  
 UPDATE T1  
 SET    First_Name = S.First_Name,  
        Last_Name  = S.Last_Name  
 FROM   T1_Numbering T1  
 JOIN   S_Numbering S ON T1.RANKID = S.RANKID  

Best regards
Melissa

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Answer 3

I believe this should work, but since I don't have your tables, it's untested.

; WITH T1_numbering AS (
    SELECT First_Name, Last_Name, row_number() OVER(ORDER BY Row_ID) AS rowno
    FROM   T1
), S_Numbering AS (
   SELECT First_Name, Last_Name, row_number() OVER(ORDER BY newid()) AS rowno
   FROM   Sample
)
UPDATE T1
SET    First_Name = S.First_Name,
       Last_Name  = S.Last_Name
FROM   T1_Numbering T1
JOIN   S_Numbering S ON T1.rowno = S.rowno

Answer 4

Hi Tom,

Removing the WHERE clause as specified results in all rows in the target table to be updated with the same first and last name.

Thoughts?

Answer 5

This is likely wrong:

WHERE
[T1].[Row_ID] = [T1].[Row_ID]