How would you think that we would know how you added a calendar to your site? We cannot see your project, your code or read your mind. Besides that, what does your calendar on your site have to do with a database?
Another one with a crappy design, available seats should be an enquiry on the Bookingtable! while using a trigger spit may fix this issue the design should be fixed to remove the need for a trigger spit
Never underestimate the power of human stupidity
Pass the update information into the stored procedure via parameters then update the relevant tables via the stored procedure.
I would tend to agree with Mycroft spit that triggers can hide things from you when you are trying to debug a problem later on.
“That which can be asserted without evidence, can be dismissed without evidence.”