Doubt's regarding the Hierarchial Queries in Oracle

Question

Hi,
i have a doubt regarding the Hierarchial Queries in Oracle.
SELECT * FROM TMP_TEST;
ID     NUMVAL     STRVAL
1     100     Hello
1     -100     World
2     1     Concatenate
2     2     In String
2     3     using Connect By
2     4     Using SYS_CONNECT_BY_PATH
i am clear with my execution of IN_Line view (mechanism how it work's) .
But i have also read about the Hierarchial queries in the Oracle product documentation's. i am also aware of the
SYS_CONNECT_BY_PATH , LEVEL & START WITH , CONNECT BY Keywords.
But i couldnot able to Manually work out as how this below Query works.
Can you please explain me how this Hieracial query works ?
SELECT ID, (SYS_CONNECT_BY_PATH(STRVAL,',')),LEVEL
FROM
SELECT ID,STRVAL,ROW_NUMBER() OVER(PARTITION BY ID ORDER BY ID) RNUM,
COUNT(*) OVER(PARTITION BY ID ORDER BY ID) CNT,NUMVAL
FROM TMP_TEST
START WITH RNUM = 1
CONNECT BY PRIOR RNUM = RNUM - 1
Many Thanks,
Rajesh.

Answer 1

Hi, Rajesh,
My first message was in response to your first message.
In your latest message, the query is:
SELECT  ID, (SYS_CONNECT_BY_PATH(STRVAL,',')),LEVEL
FROM    (
        SELECT  ID,STRVAL,ROW_NUMBER() OVER(PARTITION BY ID ORDER BY ID) RNUM,
                COUNT(*) OVER(PARTITION BY ID ORDER BY ID) CNT,NUMVAL
        FROM TMP_TEST
WHERE   RNUM = CNT
START WITH  RNUM = 1
CONNECT BY  PRIOR RNUM = RNUM - 1;It looks like you lost the second CONNECT BY condition:
AND PRIOR ID = IDPut it back: it's important.
Now you're confused about the output row:
2    ,Hello,World,using Connect By,Using SYS_CONNECT_BY_PATH   4It doesn't seem to correspond to anything results that you got when you ran the sub-query alone.
That's because the resutls from your sub-query may change every time you run it, even though the data doesn't change. The ORDER BY clauses in both of the analytic functions do not result in a complete ordering. In fact, they're completely meaningless. It never makes any sense to PARTITON BY and ORDER BY the same value; "PARTITION BY id" means that only rows with the same id will be compared to each other; you might as well say "ORDER BY 0" or "ORDER BY dmbs_random.value".
The ORDER BY clause of ROW_NUMBER whould reflect that way in which you want the results to appear within each id, for example:
ROW_NUMBER () OVER (PARTITION BY id ORDER BY UPPER (strval))Note that this is very similar to what was in my first reply.
In the COUNT function, why do you want an ORDER BY clause at all? Just say:
COUNT (*) OVER (PARTITION BY id)