How to send a request to the database through a button on a site with AJAX?

Question

visual studio

Good evening.
I am learning to make a website.
Available:

• Button
  
• Text field
  
• SQL function
  
• Field for output result
  

How to do it on ajax without refreshing the site?
I suppose everything should be very simple, but I can not find adequate understandable literature.

Answer 1

js script - ajax request - request handler on the server - data model generation - business logic layer - data access layer - sql query - business logic layer - response data model generation - request handler response - result output.
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