Extend the `order by` clause with optional `nulls first` and `nulls
last` modifiers following standard SQL semantics. Each sort key can
independently specify where `nil` values should appear in the result. By
default, ascending sorts place nulls last and descending sorts place
nulls first. An explicit nulls first or nulls last overrides this
default. The `asc` keyword is also now accepted as an explicit
alternative to the default ascending direction. Documentation and tests
were updated accordingly.
Signed-off-by: Matouš Jan Fialka <mjf@mjf.cz>
Matouš Jan Fialka
ff6854f6ee