Quote Originally Posted by chunk
please tell me what should be done in SQL, if there are two or more student who has same Top marks.
Largely depends on how you phrased your SQL, what you want to accomplish, and how your tables are structured... it's possible to return the tied records, its also possible to return just one (without going into technical details, just imagine that choice of record is up to the database), it may return an error in some joins or produce a cartesian result...

So you see, rather than asking for help for each and every query, step back and familiarize yourself with the fundamentals.