Re: Update table with random values from another table

I'm not sure if that query will do what you want, but to make it work, one thing you might try, is to pre calculate the random values for each record, then order by those, eg:

select trip_code, random() as rand from obs order by rand;

works for me, so the following might for you:

:
UPDATE
users
SET
t_firstname = x.firstname,
t_surname = x.lastname,
t_username = x.username,
t_contact = x.email
FROM
(select firstname, lastname, username, email, random() as rand
from testnames order by rand)
WHERE
t_firstname <> x.firstname;

Cheers,

Brent Wood

Brent Wood
DBA/GIS consultant
NIWA, Wellington
New Zealand
>>> Rory Campbell-Lange <rory(at)campbell-lange(dot)net> 02/17/09 4:33 PM >>>
I have a test system for which I need to replace actual user's data (in
'users') with anonymised data from another table ('testnames') on
postgres 8.3.

The tricky aspect is that each row from testnames must be randomised to
avoid each row in users being updated with the same value.

I've been trying to avoid a correlated subquery for each column I am trying
to update, and instead trying the following, which never returns. There are
2000 records in testnames and about 200 in users.

UPDATE
users
SET
t_firstname = x.firstname,
t_surname = x.lastname,
t_username = x.username,
t_contact = x.email
FROM
(select firstname, lastname, username, email
from testnames order by random()) x
WHERE
t_firstname <> x.firstname;

Any help much appreciated
Rory

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