<label>層次</label>
<select name="level" id="level">
 <option value="1">本科</option>
 <option value="2">高職（專科）</option>
</select>
<label>專業</label>
<select name="major" id="major">
 <option value="">--</option>
</select>

$("#level").click(function(){
 $.ajax({
 type:"POST",
 url:"{:U('Target/queryMajor')}",
 dataType: "json",
 data:{
 level:$('#level').val()
 },
 success:function(data){
 $("#major").empty();
 switch (data.status){
 case '1':
 $("#major").append("<option value='' >--</option>");
 $.each(data.data,function(index,val){
 $("#major").append('<option value='+val.major+' >'+val.major+'</option>');
 });
 break;
 case '0':
 $("#major").append("<option value='' >--</option>");
 break;
 }
 return false;
 }
 });
 return false;
 });

public function queryMajor()
 {
 if(I('post.level') == 1){$ccmc = '本科';}else{$ccmc = '高職（專科）';}
 $dao = M('Plan');
 $condition["ccmc"] = $ccmc;
 $record = $dao->where($condition)->field('major')->select();
 if($record != null){
 $this->ajaxReturn($record,'','1');
 }else{
 $this->ajaxReturn('','','0');
 }
 }