I have a database with a table having a big number of rows. I am fetching the data in this table and displaying it in an HTML table on a web page.
My requirement is to display 20 records initially and then when the user clicks a button labelled
This is called pagination - a quick search for "ajax pagination mysql php" or similar brings up a wide range of options. I can't recommend any particular one as your question is too broad; I can only reasonably go as far as a definition.
Internally they use the MySQL LIMIT keyword which may help give further things to search for or experiment with depending on your actual use case.