Classic SQL constructs not supported yet

[NOT] [EXISTS|INTERSECT|EXCEPT]

A syntactically available alternative is EXISTS, but it's not very useful as it doesn't support correlated subqueries. You can also rewrite it using JOIN.

NATURAL JOIN

An alternative is to explicitly list the matching columns on both sides.

NOW() / CURRENT_TIME()

An alternative is to use the functions CurrentUtcDate, CurrentUtcDatetime and CurrentUtcTimestamp.