Question

I’m doing a data migration in SQL Server 2008 R2. I’m a SQL-Server noob, but I know Ingres and MySql pretty well.

I need to set “default values” for two new fields to “the current values” from another table. Here’s my first naive attempt (how I’d do it in Ingres).

update  rk_risk
set     n_target_probability_ID = a.n_probability_ID
      , n_target_consequence_ID = a.n_consequence_ID
from    rk_assess a
WHERE   a.n_assess_id = (
    SELECT  MAX(n_assess_id)
    FROM    rk_assess a2
    WHERE   a2.n_risk_id = a.n_risk_id
);

The above query executes without error in sequel, but it sets ALL the n_target_probability_ID’s & n_target_consequence_ID’s to the same value… that of the OUTRIGHT last assessment (as apposed to “the last assessment OF THIS RISK”).

The rk_assess table contains a complete history of assessment records for rk_risks, and my mission is to “default” the new target probability & consequence column of the risk table to the values from “the current” (i.e. the last) assessment record. The rk_assess.n_assess_id column is an auto-incremented identifier (immutable once set), so the max-id should allways be the last-entered record.

I’ve had a bit of a search, both in google and SO, and tried a few different version of the query, but I’m still stuck. Here’s a couple of other epic-fails, with references.

update  rk_risk
set     n_target_probability_ID = (select a.n_probability_ID from rk_assess a where a.n_assess_id = (select max(n_assess_id) from rk_assess a2 where a2.n_risk_id = a.n_risk_id) as ca)
      , n_target_consequence_ID = (select a.n_consequence_ID from rk_assess a where a.n_assess_id = (select max(n_assess_id) from rk_assess a2 where a2.n_risk_id = a.n_risk_id) as ca)
;

http://stackoverflow.com/questions/6256844/sql-server-update-from-select

update  r 
set     r.n_target_probability_ID = ca.n_probability_ID
      , r.n_target_consequence_ID = ca.n_consequence_ID
from    rk_risk r
join    rk_assess a
on      a.n_risk_id = r.n_risk_id

select  r.n_risk_id
          , r.n_target_probability_ID, r.n_target_consequence_ID
          , ca.n_probability_ID, ca.n_consequence_ID
from    rk_risk r
join    rk_assess a
on      a.n_risk_id = r.n_risk_id

http://stackoverflow.com/questions/4024489/sql-server-max-statement-returns-multiple-results

UPDATE  rk_risk
SET     n_target_probability_ID = ca.n_probability_ID
      , n_target_consequence_ID = ca.n_consequence_ID
FROM    ( rk_assess a
INNER JOIN (
       SELECT MAX(a2.n_assess_id)
       FROM   rk_assess a2
       WHERE  a2.n_risk_id = a.n_risk_id
) ca -- current assessment

Any pointers would be greatly appreciated. Thank you all in advance, for even reading this far.

Cheers. Keith.

Answer 1

How about this:

update  rk_risk
set     n_target_probability_ID = a.n_probability_ID
      , n_target_consequence_ID = a.n_consequence_ID
from    rk_assess a
JOIN    (
    SELECT  n_risk_id, MAX(n_assess_id) max_n_assess_id
    FROM    rk_assess
    GROUP BY n_risk_id
    ) b
ON  a.n_risk_id = b.n_risk_id AND a.n_assess_id = b.max_n_assess_id
WHERE   a.n_risk_id = rk_risk.n_risk_id