尺寸数组项不插入同一个DB行

I start with the following:

<form action="" method="post" enctype="multipart/form-data" id="form">
 <?php foreach($attributes as $attribute){ ?>
  <input type="checkbox" name="attribute[][attr_id]" value="<?php echo $attribute['attribute_id']; ?>">
  <input type="text" name="attribute[][attr_name]"> value="<?php echo $attribute['attribute_name']; ?>">
 <?php } ?>
</form>

So each $attribute has a checkbox and a text input; whenever someone would check (one or more boxes) and would insert text (only to the checked items) I want to get in the DB the [attr_id] and the [attr_name] for the specific item.

So I continue with the following:

if(isset($_POST['attribute'])){
 foreach($_POST['attribute'] as $attribute){
    $attr_id = $attribute['attr_id'];
    $attr_name = $attribute['attr_name'];

    "INSERT INTO " . DB_PREFIX . "attribute_xref SET productid = '" . $productid . "', attribute_id='". $attr_id ."', attribute_name='" . $attr_name . "'";
  }
 }

But, the result is a little different as of I would have expected. Every time a box is checked and its text input is typed, their values are sent to two different DB rows:

productid   --   attribute_id   --   attribute_name
10          --       102        --        empty
10          --        0         --       somename

On the above second row the attribute_id has zero value for not being checked.

I cannot get the whole picture where is my mistake.

Finally. The tricky answer was to add an identical numerical index to the associative inputs like this:

<form action="" method="post" enctype="multipart/form-data" id="form">
  <?php foreach($attributes as $attribute){ ?>
    <input type="checkbox" name="attribute[i][attr_id]" value="<?php echo $attribute['attribute_id']; ?>">
    <input type="text" name="attribute[i][attr_name]"> value="<?php echo $attribute['attribute_name']; ?>">
  <?php } ?>
</form>

where "i" in my case would take the variable number from 'attribute_id':

<input type="checkbox" name="attribute[<?php echo $attribute['attribute_id']; ?>][attr_id]" value="<?php echo $attribute['attribute_id']; ?>">
<input type="text" name="attribute[<?php echo $attribute['attribute_id']; ?>][attr_name]"> value="<?php echo $attribute['attribute_name']; ?>">

Hopefully my answer would help somebody in the future, too.