Join index

Data Modeling
Enthusiast

Join index

Hi,

I have 3 qs:

1) Can we have JI for queries having subqueries?

2) Created JI on two tables joining a PI and non-PI and found that group amp is not used.I resorted to creating HI to solve the issue. However, I am in two minds, should I change an index totally for the 

second table or should I live with this HI?

3) In my JI design, is it always advisable to use rowid for cover  for any unforseen requirements ahead?

Thnaks and regards,

Raja