Question on a Group By/Having SQL Query

Question

I have a table which lists Users and their Status (Created, Approved, Deleted, etc.) Each status has a timestamp.
USER_ID | STATUS | TIMESTAMP
mike | Created | 12:00
mike | Entered | 1:00
mike | Approved | 3:00
mike | Deleted | 4:00
john | Created | 5:00
mary | Created | 6:00
I need to select
1) all users whose LAST status is "Approved"
2) users which have at least 1 "Created" but no "Approved"
Any ideas on how to construct these queries? Thanks

Answer 1

Hi,
803777 wrote:
Thanks a lot Frank. The 2nd Query works great, no issues.
The 1st query uses Oracle-specific keywords KEEP and DENSE_RANK. Is there a way to re-write it in standard SQL that would run on all DB servers. Thanks again for your help, very much appreciated.This is an Oracle forum. If you want something for another database, you should mention that in your first message, and not wait until someone has spent time writing code that doesn't help you.
Here's one way to get basically the same results:
SELECT    user_id
FROM       table_x
WHERE       status          = 'Approved'
AND       (user_id, tmstmp)  IN ( SELECT    user_id
                                 ,         MAX (tmstmp)
                      FROM         table_x
                      GROUP BY  user_id
;In case of a tie, this returns the user_id if any of the contenders is 'Approved'.
You could also use analytic functions instead of an IN sub-query, but I suspect the chances are greater that the IN-subquery will work on different databases.
P.S. With respect to Query #2, we're lucky because "Created" is the 1st possible status. But if I wanted to see all users who have been "Entered", let's say, but not "Approved" yet, I would have to use the having(case) syntax you mentioned, is that why you said I had to be careful? "Entered" is an intermediate status, after Created but sometime before Approved.Yes, that's exactly what I meant when I said to be careful.
Here's an example of what I meant when I said to use a CASE expression:
SELECT    user_id
FROM       table_x
WHERE       status     IN ( 'Approved', 'Created')
GROUP BY  user_id
HAVING       MIN ( CASE
                    WHEN  status = 'Created'
              THEN  1
              ELSE  0
                END            
           )          = 1
;This does not assume that the "good" status is before or after the "bad" status; and it can easily be modified to accomodate any number of "good" or "bad" values, withiout thinking of their sort order. All that matters is that the "good" ones cause the CASE expression to return 1, and the "bad" ones make it return 0.