Unsupported classic SQL constructs

Correlated EXISTS and NOT EXISTS

EXISTS and NOT EXISTS can be used with uncorrelated subqueries. Correlated subqueries are not supported. To select rows based on the presence or absence of matching rows, use LEFT SEMI JOIN or LEFT ONLY JOIN. For details, see Correlated subqueries, EXISTS, and NOT EXISTS.

INTERSECT and EXCEPT

YQL does not support INTERSECT or EXCEPT.

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.