How does order by clause works if two values are equal?

This is my NEWSPAPER table.

    National News   A   1
    Sports          D   1
    Editorials      A   12
    Business        E   1
    Weather         C   2
    Television      B   7
    Births          F   7
    Classified      F   8
    Modern Life     B   1
    Comics          C   4
    Movies          B   4
    Bridge          B   2
    Obituaries      F   6
    Doctor Is In    F   6

When i run this query

select feature,section,page from NEWSPAPER
where section = 'F'
order by page;

It gives this output

Doctor Is In    F   6
Obituaries      F   6
Births          F   7
Classified      F   8

But in Kevin Loney’s Oracle 10g Complete Reference the output is like this

Obituaries      F   6
Doctor Is In    F   6
Births          F   7
Classified      F   8

Please help me understand how is it happening?

Answer

In relational databases, tables are sets and are unordered. The order by clause is used primarily for output purposes (and a few other cases such as a subquery containing rownum).

This is a good place to start. The SQL standard does not specify what has to happen when the keys on an order by are the same. And this is for good reason. Different techniques can be used for sorting. Some might be stable (preserving original order). Some methods might not be.

Focus on whether the same rows are in the sets, not their ordering. By the way, I would consider this an unfortunate example. The book should not have ambiguous sorts in its examples.