php - Grouping rows together with the same parent-ID -

i writing private-messaging script. however, have run few problems on mysql end. i've got partially working.

an example:

messageid | parentid | subject | flags 1           null       'foobar'  2     //has been read 2           1          'foobar'  2     //has been read 3           1          'foobar'  1     //has not been read 

messageid: auto-incremented of message
parentid: messageid of first-message in thread
subject: subject (or title) of thread
flags: bit-wise flags (1 = unread; 2 = read)

the problems (which can me solve)
1. way have setup right now, script display message-thread in unread-messages page , read-messages page. goal display in unread-messages page until been read.

here query

//$_get['node'] allowed be: unread, read, or sent   $wftype = $_get['node'] == 'sent' ? 'sender' : 'recipient';   $filter = $_get['node'] == 'sent' ? '' : ' , (`flags` & '.$message_flags[$_get['node']].') != 0';   //$filter = ($_get['node'] == 'unread' || $_get['node'] == 'read') ? ($_get['node'] == 'read' ? ' , (`flags` & '.$message_flags['read'].') != 0' : ' , (`flags` & '.$message_flags['unread'].') != 0') : '';   $result = $sql->query('select `messageid`, `parent`, `senderid`, `sender`, `subject`, max(`sendtime`) `sendtime` `memberpostbox` `'.$wftype.'id` = '.$_session['client']['number'].$filter.' , (`flags` & '.$message_flags[$wftype.'_deleted'].') = 0 group `parent` order `sendtime` desc');   

will have restructure table or change how i'm doing this? or, can accomplished have now?

additional information
table-structure

create table if not exists `memberpostbox` (     `messageid` bigint(20) unsigned not null auto_increment,     `parentid` int(10) unsigned default null,     `senderid` varchar(255) collate utf8_unicode_ci not null,     `sender` varchar(255) collate utf8_unicode_ci not null,     `recipientid` varchar(255) collate utf8_unicode_ci not null,     `recipient` varchar(255) collate utf8_unicode_ci not null,     `subject` varchar(255) collate utf8_unicode_ci default null,     `message` longtext collate utf8_unicode_ci not null,     `sendtime` int(10) unsigned not null,     `flags` tinyint(3) unsigned not null default '0',     primary key  (`messageid`),     key `groupid` (`parentid`),     fulltext key `search` (`subject`,`message`)   engine=myisam  default charset=utf8 collate=utf8_unicode_ci auto_increment=22 ;   

for unread messages

'select .... memberpostbox flag=1' 

for read message

'select .... memberpostbox flag=2' 

only flag determining if message read or not, part involve display correct list..... of course have add rest of code in there.

// read $result = $sql->query(     'select         `messageid`,         `parent`,         `senderid`,        `sender`,         `subject`,         max(`sendtime`) `sendtime`      `memberpostbox`      `recipientid` = '.$_session['client']['number'].$filter.'      , `flags` = 2     , '.$message_flags[$wftype.'_deleted'].' = 0     group `parent`      order `sendtime` desc'   );