多条件查询语句，但是查询出数据后点击下一页后程序又重新将数据库中所有内容取出了。求解在线等
public function search(){
if($_POST['username']){
$where['fromusername'] = array('EQ',trim($_POST['username']));
}
if($_POST['gjc']){
$where['msgcontent'] = array('LIKE','%'.trim($_POST['gjc']).'%');
}
if($_POST['start']){
$where['posttime'] = array('LIKE', '%'.trim($_POST['start']).'%');
}
$objPage = $this->nextPage('MessageView', $where, 'id desc', 'D',15);
echo $_GET['p']."<br>";
echo $objPage['model']->getlastsql();
$this->assign('list',$objPage['list']);
$this->assign('page',$objPage['show']);
$this->assign('count',$objPage['count']);
$this->display();