#...code filling the arrays
#@A = DB list
#@B = array of data

my %seen;     # lookup table
my @aonly;    # info only in list @A
my @bonly;    # info only in list @B  

# build lookup table
@seen{@B} = ( );

foreach $item (@A) {
    push(@aonly, $item) unless exists $seen{$item};
}
%seen = ();
@seen{@A} = ( );
foreach $item (@B) {
    push(@bonly, $item) unless exists $seen{$item};
}

#@aonly = unique to DB list - @A
#@bonly = unique to array of data - @B
#continue on your merry way...