$wpdb insert not working

I've created a new meta box for my 'cases' post type. And when I publish a new 'cases' post I want to insert the meta id into a new table created by me called 'sort'. I used this code:

function save_postdata( $post_id ) {
    global $post, $new_meta_boxes, $wpdb;

    foreach ($new_meta_boxes as $meta_box) {
        if ( !wp_verify_nonce( $_POST[$meta_box['name'].'_noncename'], plugin_basename(__FILE__) )) {
                return $post_id;
            }

    if ( 'cases' == $_POST['post_type'] ) {
    if ( !current_user_can( 'edit_page', $post_id ))
        return $post_id;
        } else {
        if ( !current_user_can( 'edit_post', $post_id ))
        return $post_id;
        }

    $data = $_POST[$meta_box['name'].'_value'];

    if(get_post_meta($post_id, $meta_box['name'].'_value') == "") {

    add_post_meta($post_id, $meta_box['name'].'_value', $data, true);

    $meta_id = get_post_meta($post_id, 'm开发者_开发知识库eta_id', true);

    $wpdb->insert( 'sort', array('meta_id'=>$meta_id, 'column_order' => 1));

    }

    elseif($data != get_post_meta($post_id, $meta_box['name'].'_value', true))
    update_post_meta($post_id, $meta_box['name'].'_value', $data);

    elseif($data == "") 
    delete_post_meta($post_id, $meta_box['name'].'_value', get_post_meta($post_id, $meta_box['name'].'_value', true));



    }

}

The sort table has three fields: id, meta_id and column_order. Can someone sees what I'm doing wrong?

Make sure that on your insert statement you add 'NULL'

$wpdb->insert( 'sort', array('NULL', 'meta_id'=>$meta_id, 'column_order' => 1));

This could be causing the issue, and also make sure that it's the correct order of your columns.