$sth = $dbh->prepare('SELECT foo,bar,baz FROM widget WHERE foo=? AND bar=? AND baz=?');
$sth->execute($foo,$bar,$baz);

##</code><code>##

$sth = $dbh->prepare('SELECT foo,bar,baz FROM widget WHERE foo=? OR bar=? OR baz=?');
$sth->execute($str,$str,$str);