Table not updating with wordpress dbdelta

I have following code for creating table:

$sql = "CREATE TABLE " . $table_name . "("
         . "id mediumint(9) NOT NULL AUTO_INCREMENT, "
         . "product_id mediumint(9) DEFAULT 0 NOT NULL,"
         . "name_type mediumint(9) NOT NULL, "
         . "name_key varchar(48) NOT NULL, "
         . "valid_until datetime DEFAULT '0000-00-00 00:00:00' NOT NULL, "
         . "created_at datetime DEFAULT '0000-00-00 00:00:00' NOT NULL, "
         . "updated_at datetime DEFAULT '0000-00-00 00:00:00' NOT NULL, "
         . "UNIQUE KEY id (id)"
         . ")" . $charset_collate. ";";
require_once( ABSPATH . 'wp-admin/includes/upgrade.php' );
dbDelta( $sql );

It is working and table created.

Now I need update table and add new column (sites_list):

$sql = "CREATE TABLE " . $table_name . "("
         . "id mediumint(9) NOT NULL AUTO_INCREMENT, "
         . "product_id mediumint(9) DEFAULT 0 NOT NULL,"
         . "name_type mediumint(9) NOT NULL, "
         . "name_key varchar(48) NOT NULL, "
         . "sites_list longtext, "
         . "valid_until datetime DEFAULT '0000-00-00 00:00:00' NOT NULL, "
         . "created_at datetime DEFAULT '0000-00-00 00:00:00' NOT NULL, "
         . "updated_at datetime DEFAULT '0000-00-00 00:00:00' NOT NULL, "
         . "UNIQUE KEY id (id)"
         . ")" . $charset_collate. ";";
require_once( ABSPATH . 'wp-admin/includes/upgrade.php' );
dbDelta( $sql );

But this not work.

And I has a error:

WordPress database error: [Table 'table_name' already exists]

What is incorrect?

Thanks.

via Chebli Mohamed