DB Not UPDATE-ing

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for (@usercodelist) {
  my $SQL = "UPDATE mytable SET subscribed = '0', unsubscribedby = 'SY
+STEM' WHERE usercode = '$_' AND unsubscribedby = ''";
...
  $sth->execute || die "Could not execute SQL statement ... maybe inva
+lid?<BR>$!";
  $sth->finish();
}

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Field           DataType
-----           --------
...
subscribedby    varchar(32) binary
unsubscribedby  varchar(32) binary
unsubscribedby  varchar(32) binary

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subscribed  usercode                         subscribed by  unsubscrib
+ed by
1           7436692b91879380d9108739eb9865f5 SYSTEM

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