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my $fields = join "||'|'||", qw( field1, field2, field3);
my %set1 = map { $_ => 1 }
  get_records ( "SELECT $fields FROM table WHERE data_set = 'set1'");
...

my @set2not1 = grep { ! exists($set1{$_}) } keys %set2;
my @set1not2 = grep { ! exists($set2{$_}) } keys %set1;

CREATE VIEW set1 AS
  SELECT field1,field2,field3 FROM table WHERE data_set = 'set1';
CREATE VIEW set2 AS
  SELECT field1,field2,field3 FROM table WHERE data_set = 'set2';