正如标题所说，我有一个问题。我的插件在激活时不会创建自定义表。我的代码是：

function bsp_create_update_table() 
{

global $wpdb; //geting the acces to a wp tables
$tablename=$wpdb->prefix . "students"; //the name of a table with it\'s prefix

//checking if the table with the name we created a line above exists
if($wpdb->get_var("SHOW TABLES LIKE \'$tablename\'") != $tablename) 
 {

    //if it does not exists we create the table
    $sql="CREATE TABLE `$tablename`(
    `students_id` INT(11) NOT NULL AUTO_INCREMENT,
    `students_name` VARCHAR (50) NOT NULL,
    `students_lastname` VARCHAR (50) NOT NULL,
    `students_email` VARCHAR 850) NOT NULL, 
    `students_course` VARCHAR (100) NOT NULL,
    `students_date` DATETIME,
    PRIMARY KEY (students_id)
    );";

    //wordpress function for updating the table
    require_once(ABSPATH . \'wp-admin/includes/upgrade.php\');
    dbDelta($sql);
 }
}

当插件被激活时，并没有创建任何表，我只是不知道为什么。有什么想法吗？