Re: Re: "Oracle's ROWNUM"

Hiroshi Inoue <Inoue@tpf.co.jp> writes:
> Oracle doc says.

> If you embed the ORDER BY clause in a subquery and place the ROWNUM
> condition in the top-level query, you can force the ROWNUM condition
> to be applied after the ordering of the rows. For example, the
> following query returns the 10 smallest employee numbers. This
> is sometimes referred to as a "top-N query":

> SELECT * FROM
>    (SELECT empno FROM emp ORDER BY empno)
>    WHERE ROWNUM < 11;

This thing gets more poorly-defined every time I hear about it!?

Based on what's been said so far, ROWNUM in a WHERE clause means
something completely different from ROWNUM in the SELECT target list:
it seems they mean input row count vs output row count, respectively.
If I do
    SELECT rownum, * FROM foo WHERE rownum > 10 and rownum < 20;
will the output rows be numbered 1 to 9, or 11 to 19?  If I add a
condition, say "AND field1 < 100", to the WHERE clause, does the rownum
count include the rows rejected by the additional clause, or not?
And how do you justify any of these behaviors in a coherent fashion?

Dare I ask how it behaves in the presence of GROUP BY, HAVING,
aggregates, DISTINCT, UNION, ... ?

            regards, tom lane