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SQL Query to get maximum value based on different maximum value for multiple records

I know I can do this with a CTE or some other means, but I'm wondering if it can be done in a single select query (no subselections). I want to find the most recent crt_ts for po_nbr and then take the associated id.

Note:

The id column can't be consistent, I've simplified it for this question.

Code:

create table temp
(
    id int,
    po_nbr int,
    crt_ts datetime
)

insert into temp values (20, 100, '09/01/2009')
insert into temp values (3, 100, '09/03/2009')
insert into temp values (5, 100, '09/05/2009')
insert into temp values (6, 100, '09/07/2009')
insert into temp values (4, 200, '08/01/2009')
insert into temp values (29, 200, '08/03/2009')
insert into temp values (12, 200, '08/05/2009')
insert into temp values (18, 200, '08/07/2009')

Desired output:

id  po_nbr
---------
6   100
18  200
+2


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5 answers 


SELECT
  MAX(id) id,
  po_nbr
FROM
  temp
GROUP BY
  po_nbr

To have an appropriate date, you can do (beware, this implies a sequential id):

SELECT
  temp.id,
  temp.po_nbr,
  temp.crt_ts
FROM
  temp
  INNER JOIN (
    SELECT MAX(id) id FROM temp GROUP BY po_nbr
  ) latest ON latest.id = temp.id

Without a sequential id, it would be:



SELECT
  MAX(temp.id) id,
  temp.po_nbr,
  temp.crt_ts
FROM
  temp INNER JOIN (
    SELECT   MAX(crt_ts) crt_ts, po_nbr 
    FROM     temp i
    GROUP BY po_nbr
  ) latest ON latest.crt_ts = temp.crt_ts AND latest.po_nbr = temp.po_nbr
GROUP BY
  temp.po_nbr,
  temp.crt_ts

GROUP BY

can be omitted if no two equal dates are guaranteed in the group po_nbr

.

In the last query, pointers to crt_ts

and po_nbr

will help you build the best combined index.

+4


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try:



SELECT
    id,po_nbr --crt_ts --can show the date if you want
    FROM (SELECT 
              id,po_nbr,crt_ts
              ,ROW_NUMBER() OVER(partition BY po_nbr ORDER BY po_nbr,crt_ts DESC) AS RankValue
              FROM temp
         ) dt
    WHERE RankValue=1
+2


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SELECT 
  MAX(temp.id) AS id, det.po_nbr
FROM
  temp
  INNER JOIN (SELECT po_nbr, MAX(crt_ts) AS maxcrt_ts FROM temp GROUP BY po_nbr) AS det ON temp.po_nbr = det.po_nbr AND temp.crt_ts = maxcrt_ts
GROUP BY
  det.po_nbr
+1


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select t.id, tm.po_nbr
from  temp t
inner join (
    select po_nbr, max(crt_ts) as max_ts
    from temp 
    group by po_nbr
) tm on t.po_nbr = tm.po_nbr and t.crt_ts = max_ts
+1


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select max (id), po_nbr from tempbarry group po_nbr

0


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