Message from my past self

Comment found in my code this afternoon:

This is quite a complicated query built of lots of sub queries so if what follows is unclear, ask Jo about it (if you are future Jo reading this then bad luck, you just have to figure it out :) ).

I actually remember writing this - I wasn't convinced that anyone would be able to follow the explanation I'd written. Actually, reading it back now, it looks fine, although I'd probably use common table expressions to make the structure clearer.