If the emails are exact, you could use "distinct" in your SQL statement. E.G. something like

select distinct E_mail from table where <conditions>
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That would be the easiest approach -- let the database do the work. You could do the same work in perl using a hash to keep track of the addresses, ingoring the values of the hash.

e.g. something like (in pseudo-perl)

my %emailhash = ();

foreach $row (result_set) {
  $emailhash{$row->{email}} = 1;
}

my @unique_emails = keys %emailhash;
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Using a hash where you only care about the keys (setting the values to 1) is a common idiom for ensuring uniqueness from a list when you don't care about the order. A concise form of this idiom would be

%temp_hash = map {$_ => 1} @non_unique_list;
@unique_list = keys (%temp_hash);

# or

@unique_list = sort keys (%temp_hash);
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The latter case can be used if you want the list ordered, and can extract the order from the values of the entries themselves.

Hope this helps...

-JAS