This DBI statement is taking too long and I need to speed things up:

my $sth = $dbh->prepare("select * from campaigns where mw_export='yes'
+ and last_update > ?");
$sth->execute(last_transfer{'campaigns'});

while(my $result = $sth->fetchrow_hashref()) {

print "It takes me over 30 minutes to print this!!!\n";

}
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I have about 40,000 rows with each row containing about 200 fields. My program hangs for a loooooong time. So I know I have a few options:

1. Use indexes.
2. Use fetchrow_arrayref instead of fetchrow_hashref.

I created two indexes but didn't notice any speed improvement:

alter table campaigns add index mw_export (mw_export);
alter table campaigns add index last_update (last_update);
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Should I create a different type of index? Those are the SQL statements that I used.

The other option is to use fetchrow_arrayref. But I *need* to have $result as a hash ref. Would it be okay to convert the array ref to a hash ref? What would be the best way to do that?

I heard that fetchrow_arrayref is way faster than its hashref counterpart.

Any other things that I could try?