I would use NOT IN instead of the single value operators, like in:

@a = (1, 2, 3, 4);
@b = (6, 7, 10, 30, @a);

$a = sprintf "WHERE id NOT IN (%s)" , join(",",@a);
$b = sprintf "WHERE id NOT IN (%s)" , join(",",@b);

print $a ."\n";
print $b ."\n";
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But that assumes that you don't have any 1.4 kinds of values...

/brother t0mas