Hi Wenyu,
You can make it very easily with an boolean Attribute in your Table Entity.
Call it for example : AlreadyBooked ( default value : false)
When one of the Users reserves the table, change the boolean to true.
on the Left Side of your Page retrieve the Tables with a Xpath :
[AlreadyBooked : true]
and on the right Side the not booked tables
[AlreadyBooked : false]
Hope this Helps,
Best Regards