使用变量指定的默认值创建表

I have a php script below that creates a table. The table is created with a name according to the user email. But when the table is created, the default value for first_name which is assigned by the variable $firstname is blank. In fact, all the fields are blank. Are there any wrong with my script?

$email = $_SESSION['email'];
$firstname = $user['first_name'];

// Create database for user if not exists
$DB_CON->exec("CREATE TABLE IF NOT EXISTS `".$email."` (
  `id` INT NOT NULL AUTO_INCREMENT,
  `first_name` VARCHAR(100) NOT NULL DEFAULT '.$firstname.'
 PRIMARY KEY (`id`)
 )");

Basically thats not how Databases work but for your Problem:

$email = $_SESSION['email'];
$firstname = $user['first_name'];

// Create database for user if not exists
$DB_CON->exec("CREATE TABLE IF NOT EXISTS `".$email."` (
  `id` INT NOT NULL AUTO_INCREMENT,
  `first_name` VARCHAR(100) NOT NULL DEFAULT ".$firstname."
 PRIMARY KEY (`id`)
 );INSERT INTO `".$email."` (`id, `first_name`) VALUES(NULL, NULL)");

But as I said, thats not how databases work...

Moste likely you want to create a users table and work with that:

CREATE TABLE IF NOT EXISTS `users` (
  `id` INT NOT NULL AUTO_INCREMENT,
  `email` VARCHAR(100) NOT NULL,
  `first_name` VARCHAR(100) NOT NULL,
 PRIMARY KEY (`id`))

And then insert your data in this table.

DB_CON->exec("INSERT INTO `users` (`email`, `first_name`) VALUES (".$email.", ".firstname."")