Question:  what happens when you print out the SQL command?  Does it look like what you'd expect?

Try breaking it up into this first:

my $sql = "
    select * from (
    select * from qatest
    where ser_app_name
    like upper('%$mainsearch%')
    or att_data
    like upper('%$mainsearch%')
    or mrserver
    like upper('%$mainsearch%')
    or owner_user
    like upper('%$mainsearch%')
    or lan_serv
    like upper('%$mainsearch%')
    or s_contact
    like upper('%$mainsearch%')
    or s_provider
    like upper('%$mainsearch%')
    or prod_deliv
    like upper('%$mainsearch%')
    order by ser_app_name ASC
    ) where rownum < 31
";
print "Debug>  sql is:\n", "-" x 70, $sql, "\n", "-" x 70, "\n";
my $st = $dbh->prepare($sql);
$st->execute();
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Maybe that will expose something that shows you how to fix it.

If not, perhaps you can try sending the value displayed for $sql to the database by hand.

Update:  By the way, once you've got the problem solved, you might consider shortening it a bit:

my $like_string = "like upper('%$mainsearch%') ";
my @fields = qw(
    att_data mrserver owner_user lan_serv s_contact s_provider prod_de
+liv
);
my $like_clause = "where ser_app_name $like_string";
map { $like_clause .= " or $_ like $like_string" } @fields;


# The simplified sql statement ....
my $sql = "
    select * from (
        select * from qatest $like_clause order by ser_app_name ASC
    ) where rownum < 31
";
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