sql - Does 'Select' always order by primary key?

Question

A basic simple question for all of you DBA.

When I do a select, is it always guaranteed that my result will be ordered by the primary key, or should I specify it with an 'order by'?

I'm using Oracle as my DB.

Answer 1

No, if you do not use "order by" you are not guaranteed any ordering whatsoever. In fact, you are not guaranteed that the ordering from one query to the next will be the same. Remember that SQL is dealing with data in a set based fashion. Now, one database implementation or another may happen to provide orderings in a certain way but you should never rely on that.