Obfuscating data in postgres

Question

I'd like to obfuscate data in specific columns in postgres 9.1.

For instance, I want to give all the people a 'random' first and last name.

I can generate a pool of names to use:

select name_first into first_names from people order by random() limit 500;
select name_last into last_names from people order by random() limit 500;

Both of those queries run in about 400ms (which works fine for me, assuming they only need to run once!)

Using a regular update statement doesn't work - this just does each select once, thus gives all the people the same name:

update people
    SET name_last=(SELECT * from last_names order by random() limit 1),
    name_first=(SELECT * from first_names order by random() limit 1)
    where business_id=1;

How can I give each person a randomized name in postgres? I really don't want to do this in Ruby on Rails - I assume a pure SQL approach will be faster. However, speed isn't too much of a concern as I literally have all night for this business case.

Answer 1

        -- Invent some data
CREATE TABLE persons
        ( id SERIAL NOT NULL PRIMARY KEY
        , last_name varchar
        );

INSERT INTO persons(last_name)
SELECT 'Name_' || gs::text
FROM generate_series(1,10) gs
        ;

        -- The update
WITH swp AS (
        SELECT last_name AS new_last_name
        , rank() OVER (ORDER BY random() ) AS new_id
        FROM persons
        )
UPDATE persons dst
SET last_name = swp.new_last_name
FROM swp
WHERE swp.new_id = dst.id
        -- redundant condition: avoid updating with same value
AND swp.new_last_name <> dst.last_name
        ;

SELECT * FROM persons
        ;

RESULT:

 id | last_name 
----+-----------
  1 | Name_6
  2 | Name_4
  3 | Name_8
  4 | Name_2
  5 | Name_1
  6 | Name_10
  7 | Name_5
  8 | Name_7
  9 | Name_3
 10 | Name_9
(10 rows)