what is the need to have rajya sabha?

Answer 1

In many countries there are two chambers of parliament. That system goes back to the British (House of Commons, House of Lords). Nowadays, the function of the Upper House is to act as a watchdog over the Lower House, being able to block legislation (at least for some time) which it considers wrong.
Depending on what country we are talking about, the Upper House can also independently propose legislation. This will then be taken up and voted upon by the Lower House.

Answer 2

Just to increase the number of politicians in the country.

Answer 3

To make you ask questions