Section nullvalues-filtering you are showing filtering with equal and not equal. Wouldn't it be better if you show just one of them and the other using DISTINCT FROM, which would get different results ?
I'm demonstrating the sentence written there -
A WHERE clause that evaluates to a null value for a given row will exclude that row.
While I can do that with a single example my intent here was to also show that if one writes seemingly mutually exclusive expressions in a where clause it is possible neither expression will find a row, in this case with id=2. "p OR !p" again. I'll give this some more thought though.
In any case I do need to add a few more words framing up the examples. Probably pointing back to the cardinal rule sub-section.
