Parent/child records from same table

Question

I want to create a query that is a union such that the 2nd resultset is based on the 1st resultset. I have a table that has parent/child records in the same table.
Table: EVENTS
EVENT_ID
PARENT_EVENT_ID
CREATED_DATE
(other columns)
if PARENT_EVENT_ID is null then it is a parent record, else it is a child record. I want to select all parent records then union them with all the associated child records...something like this:
select * from EVENTS where CREATED_DATE < sysdate - 90 and PARENT_EVENT_ID is null -- All parents
union
select * from EVENTS where PARENT_EVENT_ID in (select EVENT_ID from EVENTS where CREATED_DATE < sysdate - 90 and PARENT_EVENT_ID is null) -- include any children of parents selected from above
This works but it's kind of ugly, I want to avoid using the sub-select in the 2nd because it is a repeat of the 1st statement, is there a way to alias the first statement and just refer to it in the 2nd query?

Answer 1

Hi,
kev374 wrote:
Thanks, one question...
I did a test and it seems the child rows have to also satisfy the parent row's where clause, take this example:
EVENT_ID|PARENT_EVENT_ID|CREATED_DATE
2438 | (null) | April 9 2013
2439 | 2438 | April 11 2013
2440 | 2438 | April 11 2013
select * from EVENTS where CREATED_DATE < sysdate - 9
start with EVENT_ID = 2438
connect by PARENT_EVENT_ID = prior EVENT_IDSo you've changed the condition about only wanting roots and their children, and now you want descendants at all levels.
This pulls in record #2438 (per the sysdate - 9 condition) but 2439 and 2440 are not connected. Is there a way to supress the where clause evaluation for the child records? I just want to pull ALL child records associated with the parent and only want to do the date check on the parent.Since the roots (the only rows you want to exclude) have LEVEL=1, you can get the results you requested like this:
WHERE   created_date  < SYSDATE - 9
OR      LEVEL         > 1However, since you're not ruling out the grandchildren and great-grandchildren any more, why wouldn't you just say:
SELECT  *
FROM    events
WHERE   created_date     < SYSDATE - 9
OR      parent_event_id  IS NOT NULL;?
CONNECT BY is slow. Don't use it if you don't need it.
If you x-reference my original query:
select * from EVENTS where CREATED_DATE < sysdate - 90 and PARENT_EVENT_ID is null -- All parents
union
select * from EVENTS where PARENT_EVENT_ID in (select EVENT_ID from EVENTS where CREATED_DATE < sysdate - 90 and PARENT_EVENT_ID is null) -- include any children of parents selected from above
The 2nd select does not apply the created_date < sysdate - 90 on the children but rather pulls in all related children :)Sorry; my mistake. That's what happens when you don't post sample data, and desired results; people can't test their solutions and find mistakes like that.