The 14th way is “multi way joins” also called “worst case optimal joins” which is a terrible name.

It means instead of joining tables two at a time and dealing with the temporary results along the way (eating memory), you join 3 or more tables together without the temporary results.

There is a blog post and short video of this on https://relational.ai/blog/dovetail-join and the original paper is on https://dl.acm.org/doi/pdf/10.1145/3180143

I work for RelationalAI, we and about 4 other new database companies are bringing these new join algorithms to market after ten years in academia.