Your #3 is very optimistic. You can't just remove a join (be it inner, left, or really any other type) just because you didn't refer to any fields from one of t

Your #3 is very optimistic. You can't just remove a join (be it inner, left, or really any other type) just because you didn't refer to any fields from one of the sides, and it's even harder when aggregation is in the mix. There are cases where you can without influencing the result, but they are special-case optimizations and not universally supported across databases.