How does this method handle the case of the fields?

It depends on how you set !PreserveCase when you called it.

# line 231 of DBIx::Database
 my $fields = $sth?$sth -> FETCH ($PreserveCase?'NAME':'NAME_lc'):[]  
+;
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The SQL standard does not specify whether field names are stored in lower, mixed, or upper case and each DBMS has its own choice. (This is how they're stored and returned from a query , not how they're used in SQL which must be case insensitive unless quoted)

Actually Oracle always returns field names in uppercase

DBI makes this explicit with (and recommends the use of) $sth->{NAME_lc} and $sth->{NAME_uc} rather than the kind of generic query that Recordset seems to use.

After looking at line 231, you _know_ what Recordset does. And you know that !PreserveCase allows one to force lowercase or take the field name as it is... it does not appear to support NAME_uc

Carter's compass: I know I'm on the right track when by deleting something, I'm adding functionality.