目前我在自定义函数方面遇到了一个问题，一旦向数据库中添加了一个值，我就无法删除该值，解决这个问题的最佳方法是什么？

基本上，我已经为游戏数据库创建了一个自定义帖子类型，添加游戏时有几个自定义帖子功能；游戏开发者、发布者、评论分数和评论URL，现在如果我输入一个测试URL，它将保存该URL，但当我尝试删除它时，它仍会出现，并且不会保存删除的值。

下面是我使用的代码：

<?php
function display_games_database_meta_box( $games_database ) {
// Retrieve information from the game
$game_publisher = esc_html( get_post_meta( $games_database->ID, \'game_publisher\', true     ) );
$game_developer = esc_html( get_post_meta( $games_database->ID, \'game_developer\', true ) );
$game_rating = intval( get_post_meta( $games_database->ID, \'game_rating\', true ) );
$game_review_link = esc_html( get_post_meta( $games_database->ID, \'game_review_link\', true ) );
$game_release = esc_html( get_post_meta( $games_database->ID, \'game_release\', true ) );
?>
<table>
    <tr>
        <td style="width: 100%">Game Publisher</td>
        <td><input type="text" size="80" name="games_database_game_publisher" value="<?    php echo $game_publisher; ?>" /></td>
    </tr>
    <tr>
        <td style="width: 100%">Game Developer</td>
        <td><input type="text" size="80" name="games_database_game_developer" value="<?php echo $game_developer; ?>" /></td>
    </tr>
    <tr>
        <td style="width: 150px">Game Rating</td>
        <td>
            <select style="width: 100px" name="games_database_rating">
            <option value="No Score">No Score</option>
            <?php
            // Generate all items of drop-down list
            for ( $rating = 10; $rating >= 1; $rating -- ) {
            ?>
                <option value="<?php echo $rating; ?>" <?php echo selected( $rating, $game_rating ); ?>>
                <?php echo $rating; ?>/10<?php } ?>

            </select>
        </td>
    </tr>
    <tr>
        <td style="width: 100%">Review Link (Use the full URL)</td>
        <td><input type="text" size="80" name="games_database_review_link" value="<?php echo $game_review_link; ?>" /></td>
    </tr>        
    <tr>
        <td style="width: 100%">Game Release Date (Format: June 26th 2013)</td>
        <td><input type="text" size="80" name="games_database_game_release" value="<?    php echo $game_release; ?>" /></td>
    </tr>
</table>
<?php
}
?>
<?php
// Adds and saves the game to the database
add_action( \'save_post\', \'add_games_database_fields\', 10, 4 );
function add_games_database_fields( $games_database_id, $games_database ) {
// Check post type for games
if ( $games_database->post_type == \'games_database\' ) {
    // Store data in post meta table if present in post data
    if ( isset( $_POST[\'games_database_game_publisher\'] ) && $_POST[\'games_database_game_publisher\'] != \'\' ) {
        update_post_meta( $games_database_id, \'game_publisher\', $_POST[\'games_database_game_publisher\'] );
    }
    if ( isset( $_POST[\'games_database_game_developer\'] ) && $_POST[\'games_database_game_developer\'] != \'\' ) {
        update_post_meta( $games_database_id, \'game_developer\', $_POST[\'games_database_game_developer\'] );
    }
    if ( isset( $_POST[\'games_database_rating\'] ) && $_POST[\'games_database_rating\'] != \'\' ) {
        update_post_meta( $games_database_id, \'game_rating\', $_POST[\'games_database_rating\'] );
    }
    if ( isset( $_POST[\'games_database_review_link\'] ) && $_POST[\'games_database_review_link\'] != \'\' ) {
        update_post_meta( $games_database_id, \'game_review_link\', $_POST[\'games_database_review_link\'] );
    }
    if ( isset( $_POST[\'games_database_game_release\'] ) && $_POST[\'games_database_game_release\'] != \'\' ) {
        update_post_meta( $games_database_id, \'game_release\', $_POST[\'games_database_game_release\'] );
    }
}
}