RE: ROWNUM is driving me nuts - queries suggested produced no res

From: Mercadante, Thomas F <NDATFM_at_labor.state.ny.us>
Date: Wed, 09 Jul 2003 08:40:54 -0700
Message-ID: <F001.005C4146.20030709083439@fatcity.com>

MaryAnn,

the best way to understand rownum is to do the following:

SQL> SELECT ROWNUM, GENDER
2 FROM (SELECT ROWNUM, GENDER

  3          FROM   EMP2
  4          WHERE  ROWNUM <= 20)

You will quickly see that, no matter how you order the result set, the first record returned is rownum #1, second is rownum #2 etc. The rownum value is assigned as rows are RETURNED or DISPLAYED, not as they are selected.

when you run your original query:

SQL> SELECT ROWNUM, GENDER
2 FROM (SELECT ROWNUM, GENDER

  3          FROM   EMP2
  4          WHERE  ROWNUM <= 20)

5 WHERE ROWNUM > 10; you should *not* get any rows because the first row returned has a value of 1 - hece you get nothing. the next row returned gets the value of 1 - again, nothing gets shown.

just what is it you want to return in your query?

Tom Mercadante
Oracle Certified Professional

-----Original Message-----
Sent: Wednesday, July 09, 2003 12:19 PM
To: Multiple recipients of list ORACLE-L results

I definitely dont fully understand ROWNUM yet, and you guys so far provided more info than a couple of books by Oracle, that I have here. For a second I thought I'm beginning to get it, but the queries suggested produced no results...

SQL> SELECT ROWNUM, GENDER
2 FROM (SELECT ROWNUM, GENDER

  3          FROM   EMP2
  4          WHERE  ROWNUM <= 20)

5 WHERE ROWNUM > 10; no rows selected

SQL> SELECT r, GENDER
2 FROM (SELECT ROWNUM r, GENDER

  3          FROM   EMP2
  4          WHERE  ROWNUM <= 20)

5 WHERE ROWNUM > 10; no rows selected

SQL> SELECT r "ROWNUM", GENDER
2 FROM (SELECT ROWNUM r, GENDER

  3          FROM   EMP2
  4          WHERE  ROWNUM <= 20)

5 WHERE ROWNUM > 10; no rows selected

SQL> ... so, any help is appreciated - rownum is driving me nuts...

thx
maa

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Author: MaryAnn Atkinson
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Author: Mercadante, Thomas F
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