Javascript jQuery验证以选择至少一个复选框

我已经编写了以下代码来选择多个复选框，还需要验证至少选择了一个复选框。在下面的代码中，如果我删除

onsubmit=“return validate\u form（）”

，则向数据库提交数据是有效的。但我想验证至少选中了一个复选框

代码如下：

<?php
$link=mysql_connect("localhost","root","") or die("cant connect");

mysql_select_db("country_ajax",$link) or die("cant select db");
extract($_POST);
$check_exist_qry="select * from language";
$run_qry=mysql_query($check_exist_qry);
$total_found=mysql_num_rows($run_qry);
if($total_found >0)
{
    $my_value=mysql_fetch_assoc($run_qry);
    $my_stored_language=explode(',',$my_value['language_name']);
}

if(isset($submit))
{
    $fname=$_POST['fname'];
    $sname=$_POST['sname'];
    $all_language_value = implode(",",$_POST['language']);
    if($total_found >0)
    {
        //update
        $upd_qry="UPDATE language SET language_name='".$all_language_value."' where member_id = 75";
        mysql_query($upd_qry);

    }
    else
    {
        //insert
        $ins_qry="INSERT INTO language(language_name) VALUES('".$all_language_value."') where member_id = 75";
        mysql_query($ins_qry);
    }
}

?>
<form method="post" action="" onsubmit="return validate_form()";>
<input type="text" name="fname"/><br>
<input type="text" name="sname"/><br>
languahe you know <br/>
    <input type="checkbox" name="language[]" value="1" <?php if(in_array(1,$my_stored_language)){echo "checked";}?>><label>PHP</label><br>
    <input type="checkbox" name="language[]" value="2" <?php if(in_array(2,$my_stored_language)){echo "checked";}?>><label>Java</label><br>
    <input type="checkbox" name="language[]" value="3" <?php if(in_array(3,$my_stored_language)){echo "checked";}?>><label>c</label><br>
    <input type="checkbox" name="language[]" value="4" <?php if(in_array(4,$my_stored_language)){echo "checked";}?>><label>javascript</label><br>
    <input type="checkbox" name="language[]" value="5" <?php if(in_array(5,$my_stored_language)){echo "checked";}?>><label>c#</label><br>
    <input type="checkbox" name="language[]" value="6" <?php if(in_array(6,$my_stored_language)){echo "checked";}?>><label>.net</label><br>


    <input type="submit" name="submit" value="submit">
</form>
<script>
function validate_form()
{
valid = true;

if($('input[type=checkbox]:checked').length == 0)
{
    alert ( "ERROR! Please select at least one checkbox" );
    valid = false;
}

return valid;
}
</script>

试试这个。
页面中是否包含jQuery。。。浏览器中是否存在任何控制台错误-看起来很好-确保jQuery像

    function validate_form()
    {
    valid = true;
    $('form').find('input[type=checkbox]').each(function(){
        if($('input[type=checkbox]:checked').length == 0)
        {
            alert ( "ERROR! Please select at least one checkbox" );
            valid = false;
        }
     )};


return valid;
}