
select * from emp order by 5 desc; in the above what is the meaning of 5, and what its functionality.........

The query you provided should be like this:
select * from emp order by id desc limit 5;
Since "order by" can only be implement on any database table field & also a field name cannot be 5.
If you are facing any programming issue, such as compilation errors or not able to find the code you are looking for.
Ask your questions, our development team will try to give answers to your questions.