17307/Mysore-Bagalkot Basava Express is the longest distance covering train within Karnataka which takes 1020 km, by 21hr 30 min time
It is a South Western Railway Zone train, interesting fact is it passes through 2 state (Andhra Pradesh and Maharashtra (Solapur) to reach Bagalkot in Karnataka.
I think so no train can make this much record covering 1000 km plus distance within Karnataka
Next 2nd long distance train is 16566/Mangalore Central-Yesvantpur Weekly Express which takes 833 km when shorter route is 363 km
Travel Duration:- 16 hr 53 min
This train acts as a alternative train because of its route, its goes via Palakkad, Salem, Krishnarajapuram instead of Ghat section route via Subramanya Road, Hassan Route.
Very less popular train among Mangalore to Bangalore section.
3rd Train is 16592/Mysore Hubli Hampi Express via Guntakal
Travel Duration:- 15 hr 30 min and 679 km via Bangalore, Guntakal, Hospete when shorter route is 473 km.
Very useful train for Hampi going tourist destination from Mysore and also Ballary, Gadag.
4th long distance train is 16227/Mysore-Talguppa Express via Ksr Bengaluru
It takes 12 hours approx, and covers 508 km when shorter route is 373 km
It's a overnight train between Mysore and Talguppa, slow journey, but peacefully able to sleep.