Why did you opt not to do something like

my %db_results;
my @parm_cols = qw( abc ghi jkl def );
my $select = 'SELECT '.join(',', @parm_cols);
# Read db
@db_results{@parm_cols} = (4,3,2,1);
print join(' ', @db_results{@parm_cols}), "\n";
# Or index individual columns at will
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?

Your columns are specified once, so any changing happens in one place.