select maximum value in inner query < another in an outer query

Question

I have two auditing tables: Trip_aud and Event_aud. They were created in Envers, but I'm querying them with SQL. Their are basically the same as the domain tables, except for a revision value which is incremented every time there is a change and some tuple is inserted in an auditing table.

When Trip changes from a certain status(PLANNING -> EXECUTING), I store its current revision, so after that I can compare what was executed (say, leaving time) with what was planned. These events (leaving, stopping, waiting...) are stored in Event, with a pointer to Trip. Events, too, are audited.

Envers works like a CVS system: if I query for some element at a given revision, it searches for the tuple which has the maximum revision less than the given revision. The revision I'm interested is the one at Trip, stored when it changes state. How can I select all events from a trip in a given revision?

Here's how the tables look like. org_rev is the trip revision where the status changes.

Trip_aud
id  | rev | status   | org_rev | other columns...
----|-----|----------|---------|---------------
 1  |  1  |CREATED   |  NULL   |
 1  |  2  |OPTIMIZING|  NULL   |
 1  |  3  |PLANNED   |  NULL   |
 1  | ... |   ...    |  NULL   |
 1  |  44 |EXECUTING |   44    |
 1  |  58 |FINISHED  |   44    |

Event_aud
id  | trip_id | rev | start_time | other columns...
----|---------|-----|------------|---------------
 1  |    1    |  1  | 02:35:12   |
 2  |    1    |  1  | 03:14:84   |
 3  |    1    |  1  | 12:31:02   |
 1  |    1    |  2  | 04:00:00   |
 2  |    1    |  5  | 03:00:15   |
 2  |    1    |  10 | 05:49:59   |
 1  |    1    |  40 | 06:00:00   |
 1  |    1    |  58 | 06:07:39   |

If I want the trip and events at revision 3, I get

Trip_aud
id  | rev | status   | org_rev | other columns...
----|-----|----------|---------|---------------
 1  |  3  |PLANNED   |  NULL   | ...

 Event_aud
id  | trip_id | rev | start_time | other columns...
----|---------|-----|------------|---------------
 1  |    1    |  2  | 04:00:00   |
 2  |    1    |  1  | 03:14:84   |
 3  |    1    |  1  | 12:31:02   |

In revision 44, when planning was finished, it is

Trip_aud
id  | rev | status   | org_rev | other columns...
----|-----|----------|---------|---------------
 1  |  44 |EXECUTING |   44    |

Event_aud
id  | trip_id | rev | start_time | other columns...
----|---------|-----|------------|---------------
 1  |    1    |  40 | 06:00:00   |
 2  |    1    |  10 | 05:49:59   |
 3  |    1    |  1  | 12:31:02   |

I have made the following query to compare planning and executed, but it returns nothing! It makes a self join in EVENT_AUD, evicts tuple duplicates that differ only on their revision order and tries to select the maximum rev less than org_rev at trip.

 select t.id, planned.start_time, realized.start_time
 from 
     TRIP t
     inner join EVENT realized on realized.trip_id = t.id
     inner join EVENT_AUD planned on planned.id = realized.id
 where
     planned.id in
     (
         select ea1.id
         from
             EVENT_AUD ea1
             inner join EVENT_AUD ea2 on ea1.id = ea2.id
         where
            ea1.rev > ea2.rev
         group by ea1.id
         having max(ea1.rev) < t.org_rev
    )
    and t.id = {something given outside}

Curiously, if I replace t.org_rev with 44, it works! What am I doing wrong?

Thanks for any help!

META: is it expected to provide a little database example in CSV, XML, INCLUDE INTOs or whatever so people can test the SQL I'm asking for? How can I attach to the question?

META answer: yes, it helps a lot when you provide the SQL to create your data. You can edit your question, or another good way is to paste your code into a "gist" here: https://gist.github.com/ and then put the gist URL into the question. — joelparkerhenderson, Mar 30 '12 at 11:13

Nikola Markovinović · Accepted Answer · 2012-03-30T11:31:47.617

I think that you need to join ea1 and ea2 on trip id too, because this way max gives maximum rev for all events. This join is also missing between event and event_aud. Correlated subquery needs

where ea1.trip_id = t.id

UPDATE:

I did not understand logic in planned in (select ...) so I changed it to not exists:

 select t.id TripID, 
        planned.id pid, 
        planned.rev, 
        planned.start_time pst, 
        realized.start_time rst
 from 
     TRIP t
     inner join EVENT realized 
        on realized.trip_id = t.id
     inner join EVENT_AUD planned 
        on planned.id = realized.id
           and realized.trip_id = planned.trip_id
        -- Eliminate higher revisions
           and planned.rev < t.org_rev
 where not exists (select null 
             from event_aud ea
            where ea.trip_id = planned.trip_id
              and ea.id = planned.id
        -- Eliminate higher revisions
              and ea.rev < t.org_rev
        -- If there is higher revision than current not exists evaluates to false
              and ea.rev > planned.rev)
    and t.id = 1
order by 1, 2

Full query is at Sql Fiddle

select maximum value in inner query < another in an outer query

1 Answers1