How to Search engine works (ex:google)

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C#

ASP.NET

hi all,

can i know how to search engine works?

As a Developer:
any searching functionality we thought to search with in databse(we have only one onedatabse)=>some tables(within databse we have tables)=>search every tables
if matching then results will be dispalyed other wise there is no results.

As a Google (Search Engine)
have many(thousands) databses but we(any one type any matter) any matter give it related results.

how it's possible? how it's work?

i mean how to search every databse and every tables? is there any functionality to search every databse and tables.

i want to know how it's work?

let me know detaily how it's work?explain..........theory + example code

Thanks to advance.............