Our optimizations get in the way of Salesforce pushdown. Specifically rewriting like when possible to = and converting outer joins to inner joins. In both cases we would need to not perform the optimization in the first place or convert into an acceptable form prior to pushdown.

The next is that salesforce, while requiring key criteria also allows other criteria in the left outer join on clause (which would be the same as having criteria on the nested relationship query in the salesforce query). With the capabilities as currently defined this would cause the query to not be pushed down. We should consider adding a relational supported join criteria type that requires key criteria but allows for outside criteria. Also we should treat the lack of inner join support to mean that criteria on the inner side of an outer join cannot be pushed.