Question

Given a table of

Name   Age
Bob    30
Paul   35
John   35

and a statement

select * from table ORDER BY Age DESC

What is the ordering of the resulting table?

Name   Age
Paul   35
John   35
Bob    30

or

Name   Age
John   35
Paul   35
Bob    30

or undefined behaviour?

Answer 1

It’s guaranteed that Bob will be the last row of the resultset. The relative ordering of the other rows isn’t guaranteed in any way.

If you need guaranteed ordering then you need to be explicit about it. For example:

SELECT *
FROM table
ORDER BY age DESC,
         name ASC