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

B RIGHT JOIN A is the same as A LEFT JOIN B

B RIGHT JOIN A reads: B ON RIGHT, THEN JOINS A. means the A is in left side of data set. just the same as A LEFT JOIN B

There are no performance that can be gained if you'll rearrange LEFT JOINs to RIGHT.

The only reasons I can think of why one would use RIGHT JOIN is if you are type of person that like to think from inside side out (select * from detail right join header). It's like others like little-endian, others like big-endian, others like top down design, others like bottom up design.

The other one is if you already have a humongous query where you want to add another table, when it's a pain in the neck to rearrange the query, so just plug the table to existing query using RIGHT JOIN.

The only reason I can think of to use RIGHT OUTER JOIN is to try to make your SQL more self-documenting.

You might possibly want to use left joins for queries that have null rows in the dependent (many) side of one-to-many relationships and right joins on those queries that generate null rows in the independent side.

This can also occur in generated code or if a shop's coding requirements specify the order of declaration of tables in the FROM clause.