When or why would you use a right outer join instead of left?

Question

Wikipedia states:

\"In practice, explicit right outer joins are rarely used, since they can always be replaced with left outer joins and provide no additional functi

Answer 1

I've not really had to think much on the right join but I suppose that I have not in nearly 20 years of writing SQL queries, come across a sound justification for using one. I've certainly seen plenty of them I'd guess arising from where developers have used built-in query builders.

Whenever I've encountered one, I've rewritten the query to eliminate it - I've found they just require too much additional mental energy to learn or re-learn if you haven't visited the query for some time and it hasn't been uncommon for the intent of the query to become lost or return incorrect results - and it's usually this incorrectness that has led to requests for me to review why the queries weren't working.

In thinking about it, once you introduce a right-join, you now have what I'd consider competing branches of logic which need to meet in the middle. If additional requirements/conditions are introduced, both of these branches may be further extended and you now have more complexity you're having to juggle to ensure that one branch isn't giving rise to incorrect results.

Further, once you introduce a right join, other less-experienced developers that work on the query later may simply bolt on additional tables to the right-join portion of the query and in doing so, expanding competing logic flows that still need to meet in the middle; or in some cases I've seen, start nesting views because they don't want to touch the original logic, perhaps in part, this is because they may not understand the query or the business rules that were in place that drove the logic.