- my ($tid, $sid) = $dbh->selectrow_array(<<'', undef, $mid);
-SELECT tid,sid FROM over
-LEFT JOIN id2num ON over.num = id2num.num
-LEFT JOIN msgid ON id2num.id = msgid.id
-WHERE msgid.mid = ? AND over.num > 0
-LIMIT 1
+
+ my $id = $dbh->selectrow_array(<<'', undef, $mid);
+SELECT id FROM msgid WHERE mid = ? LIMIT 1
+
+ defined $id or return nothing;
+
+ my $num = $dbh->selectrow_array(<<'', undef, $id);
+SELECT num FROM id2num WHERE id = ? AND num > 0
+ORDER BY num ASC LIMIT 1
+
+ defined $num or return nothing;
+
+ my ($tid, $sid) = $dbh->selectrow_array(<<'', undef, $num);
+SELECT tid,sid FROM over WHERE num = ? LIMIT 1
+
+ defined $tid or return nothing; # $sid may be undef