You don't need any additional statements,
merge by does a full join by default.
merge by does however require that tables/views you merge be sorted or indexed by the merge keys before-hand, whereas sql can sort (or do other things) on the fly if needed.
One case where the results will be different between
merge by and sql are if you have non-unique keys in both tables as
merge by does not do cartesian products.
Another case is if you have identically named variables, as sql will keep the values from the first table, whereas
merge by will overwrite them with the second table's values.