如何使用mysqli在数据库中添加生成的文本框的值

此代码以某种方式只存储最后一个文本框的值。当我们生成3个文本框时，数据库中只存储值3rd，而不是全部。我想将所有生成的文本框值存储在数据库中

 <?php if(isset($_POST['submit'])){
$num_cat = $_POST['num_cat'];
$text = $_POST['category'];
foreach ($text as $key) {
  // echo $key."'n";
}
$insertquery = mysqli_query($con, "INSERT INTO accounts (accountusername, accountemail) VALUES('".$num_cat."', '".$key."')");
if(!$insertquery){
  echo "Error".mysqli_error($con);
}
} ?>
<script type="text/javascript">
    //when the webpage has loaded do this
    $(document).ready(function() {  
        //if the value within the dropdown box has changed then run this code            
        $('#num_cat').change(function(){
            //get the number of fields required from the dropdown box
            var num = $('#num_cat').val();                  
            var i = 0; //integer variable for 'for' loop
            var textboxes = ''; //string variable for html code for fields 
            //loop through to add the number of fields specified
            for (i=1;i<=num;i++) {
                //concatinate number of fields to a variable
                textboxes += 'Category'+i+': <input type="text" name="category[]' + i + '" placeholder = "category_' + i + '" /><br/>'; 
            }
            //insert this html code into the div with id catList
            $('#catList').html(textboxes);
        });
    }); 
</script>

 <form method="post" action="">
    Number of fields required:      
    <select id="num_cat" name="num_cat">
        <option value="0">- SELECT -</option>
        <option value="1">1</option>
        <option value="2">2</option>
        <option value="3">3</option>
        <option value="4">4</option>
        <option value="5">5</option>
        <option value="6">6</option>
        <option value="7">7</option>
        <option value="8">8</option>
        <option value="9">9</option>
        <option value="10">10</option>
    </select>
    <div id="catList"></div>
    <input type="submit" name="submit" value="Submit"/>
</form>