yii multi & reverse dependant dropdown menu - ajax

Question

Since this is my first question, do tell me if i miss anything..
I have 3 dropdown menu which are dependant..
1st dropdown is to select table names which will automatically update 2nd dropdown menu which will list attributes names based on the selected table name.. this are successfully implemented..
in 2nd dropdown menu, after selecting the attributes names, user will need to click on the submit button.. when submitting, it will update 2nd dropdown menu to exclude the previously selected attribute names, and will send the selected attribute names to the 3rd dropdown menu..
Updating the 2nd dropdown menu to exclude the previously selected attributes are successfully implemented..
But updating the 3rd dropdown menu are no success..
Do guide me where I'm missing.. I'm still new with Yii so pls be patient with me ok =D
Codes on the controller:
public function actionLoadColumn()
{
$getCol = array();
$col = array();
$getTblNm[] = $_POST['tableNm'];
if(isset($_POST['columnDD'])){
$getCol[]=$_POST['columnDD'];
}
foreach($getCol as $getColKey=>$getColVal){
foreach($getColVal as $getColKey1=>$getColVal1){
$col[]=$getColVal1;
}
}
$getAttr = array();
foreach($getTblNm as $tblKey=> $tbl){
foreach( $tbl as $data){
$model1 = new $data;
$getColumn = $model1->attributes;
foreach($getColumn as $key=>$val){
$getAttr[]=$key;
}
$getAttr = array_combine($getAttr, $getAttr);
unset($getAttr['created_by'],$getAttr['created_at'],$getAttr['updated_by'],$getAttr['updated_at']);
foreach($col as $colKey=>$colVal){
unset($getAttr[$colVal]);
}
}
}
//var_dump($getAttr);
foreach($getAttr as $value=>$city_name)
echo CHtml::tag('option', array('value'=>$value),CHtml::encode($city_name),true);
var_dump($col);
if(isset($_POST['columnDD'])){
echo CHtml::dropDownList('selCol','', $col,//CHTML::listData($getTNm,'tableNm','tableNm'),
array(
'multiple'=>'multiple',
'size'=>15,
//'prompt'=>'SELECT TABLES',
'ajax' => array(
'type'=>'POST',
//'url'=>CController::createUrl('loadcolumn'),
//'update'=>'#columnDD',
//'data'=>array('tableNm'=>'js:this.value'),
)
)
);
}
//foreach($col as $cVal=>$cKey)
// echo CHtml::tag('option', array('value'=>$cVal, 'update'=>'selCol'),CHtml::encode($cKey),true);
}
codes on the view:
<div class="form">
<?php $form=$this->beginWidget('CActiveForm', array(
'id'=>'base-company-reg-form',
'enableAjaxValidation'=>false,
));
//xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx----START----xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
echo '<table><tr><td>1. Select tables</td><td></td><td>2. Select columns</td><td></td><td>3. Arrange columns</td></tr><tr><td>';
echo CHtml::dropDownList('tableNm[]','', $getTNm,//CHTML::listData($getTNm,'tableNm','tableNm'),
array(
'multiple'=>'multiple',
'size'=>15,
//'prompt'=>'SELECT TABLES',
'ajax' => array(
'type'=>'POST',
'url'=>CController::createUrl('loadcolumn'),
'update'=>'#columnDD',
//'data'=>array('tableNm'=>'js:this.value'),
)
)
);
echo '</td><td>';
echo'=';
echo '</td><td>';
echo CHtml::dropDownList('columnDD[]','', array(), array('multiple'=>'multiple', 'size'=>'15'));
echo '</td><td>';
echo CHtml::ajaxSubmitButton('>>>',Yii::app()->createUrl('baseCentre/loadcolumn'),
array(
'type'=>'POST',
'update'=>'#columnDD',
)
);
echo '</td><td>';
//echo CHtml::dropDownList('selCol[]','', array(), array('multiple'=>'multiple', 'size'=>'15'));
echo '</td></tr></table>';
//xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx----END----xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
?>
<?php
$this->endWidget();
?>
</div>