Checks whether a function identifier referenced by an UnresolvedFunction is defined in the
function registry. Note that this rule doesn't try to resolve the UnresolvedFunction. It
only performs simple existence check according to the function identifier to quickly identify
undefined functions without triggering relation resolution, which may incur potentially
expensive partition/schema discovery process in some cases.
Checks whether a function identifier referenced by an UnresolvedFunction is defined in the function registry. Note that this rule doesn't try to resolve the UnresolvedFunction. It only performs simple existence check according to the function identifier to quickly identify undefined functions without triggering relation resolution, which may incur potentially expensive partition/schema discovery process in some cases.
https://issues.apache.org/jira/browse/SPARK-19737
ResolveFunctions