Complex query/subquery/join problem

Question

Hi,
i need to retrieve information from our database in one single dataset but i can't get it all together...
Here's the situation:
We have several linked tables:
Workorder (wo_operation)
-woo_key
Workorder_task (wo_task)
-wot_key -> PK
-woo_key -> FK_woo
Workorder_task_labor (wo_task_labor)
-wtl_key -> PK
-wot_key -> FK_wot
-start_time -> essential field
I'm running a query which retrieves records from the Workorder (wo_operation) table like this (this one works nicely, don't mind the other joins):
SELECT
rownum num,
woo.woo_auto_key,
woo.si_number,
apc.application_code,
cmp.company_name,
woo.company_ref_number,
view_wo.serial_number,
view_wo.part_number,
view_wo.description part_description,
wos.description status_description
FROM (((((wo_operation woo INNER JOIN view_spb_wo_maincomponent view_wo ON woo.woo_auto_key = view_wo.woo_auto_key)
LEFT JOIN wo_status wos ON woo.wos_auto_key = wos.wos_auto_key)
INNER JOIN parts_master pnm ON woo.pnm_auto_key = pnm.pnm_auto_key)
INNER JOIN application_codes apc ON pnm.apc_auto_key = apc.apc_auto_key)
INNER JOIN companies cmp ON woo.cmp_auto_key = cmp.cmp_auto_key)
WHERE woo.wos_auto_key IS NULL OR woo.wos_auto_key not IN (2, 10)
Now here's the problem. I need to add one more column which shows the last task (max(wo_task_labor.start_time)) that people have been working on (wo_task.description).
Wo_task is linked to wo_operation on WOO_KEY (many TO one)
Wo_task_labor is linked to Wo_task on WOT_KEY (zero or many TO one)
So I need to find the MAX wo_task_labor.START_TIME and then Select the wo_task.description with that start_time. BUT since the relation is ZERO OR MORE to ONE it could be that there isn't even a START_TIME available for Max() function.......
Is there anybody who could send me in the right direction???

Answer 1

Hmmz ok, I just finished a more readable problem description.. Were you absolutely certain that my problem needs another approach?
here's the problem again:
Situation:
wo_operation
| Woo_auto_key | Si_number |
| 1            | w100      |
| 2            | w105      |
| 3            | w200      |
wo_task
| Wot_auto_key | Woo_auto_key | Description |
| 1            | 1            | OPENING     |
| 2            | 1            | INSPECT     |
| 3            | 2            | OPENING     |
| 4            | 2            | REJECT      |
| 5            | 3            | OPENING     |
Wo_task_labor
| Wtl_auto_key | Wot_auto_key | Start_time | Stop_time |
| 1            | 1            | 7:00       | 7:05      |
| 2            | 1            | 11:45      | 12:00     |
| 3            | 2            | 10:00      | 10:15     |
| 4            | 2            | 11:00      | 11:20     |
| 5            | 2            | 11:35      | 11:40     |
| 6            | 3            | 9:00       | 9:15      |
| 7            | 3            | 9:30       | 9:40      |
| 7            | 3            | 9:45       | 9:50      |
| 8            | 4            | 9:00       | 10:00     |
| 9            | 4            | 10:15      | 10:30     |
Query:
SELECT
     woo.si_number
FROM
     wo_operation woo
Result:
| SI_NUMBER |
| w100      |
| w105      |
| w200      |
My needed result:
| SI_NUMBER | DESCRIPTION      |
| w100      | OPENING          | -> last labor is wtl_auto_key 2 from 11:45 to 12:00
| w105      | REJECT           | -> last labor is wtl_auto_key 9 from 10:15 to 10:30
| w200      | (null) or 'none' | -> last labor is not available since there is no labor record
How can this be done querywise?
Message was edited by:
user574699