<label>层次</label>
<select name="level" id="level">
 <option value="1">本科</option>
 <option value="2">高职（专科）</option>
</select>
<label>专业</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 = '高职（专科）';}
 $dao = M('Plan');
 $condition["ccmc"] = $ccmc;
 $record = $dao->where($condition)->field('major')->select();
 if($record != null){
 $this->ajaxReturn($record,'','1');
 }else{
 $this->ajaxReturn('','','0');
 }
 }