怎么在搜索表单提交搜索按钮时如果字符为空弹出警告？ [复制链接]

1.怎么在搜索表单提交搜索按钮时如果字符为空弹出警告？2.搜索时如果没有匹配项还是会出来空白页，怎么让这个空白页也能弹出提示无结果或是无此信息之类的提示呢？
代码如下：
<form action="/e/search/" target="zdy_search" method="get" name="S_feedback">
    <div style="background:url(/e/upload/s1/fck/image/2013-08/chaxun.png)center center no-repeat; no-repeat 0 0">
    <div style="text-align: center;"><br />
    <br />
    <br />
    <br />
    <br />
    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 姓&nbsp;&nbsp; 名：<input type="text" maxlength="50" value="" id="pa_truename" name="pa_truename" class="tb" /><br />
    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;     查询码：<input type="text" maxlength="50" value="" id="code" name="code" class="tb" /><br />
    <!--以上html代码可根据需要删除和修改-->&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <input type="hidden" value="113" name="modelid" /><input type="hidden" value="1" name="siteid" /><input type="submit" value=" 查询 " class="bt" /><br />
    <br />
    <br />
    </div>
    </div>
</form>