joins-nested loops,hash or merge

[mahajanakhil198]

Yes Indexes affect performance of joins. Assume this logic where
For (in 1 to 1000)
select salary from emp where emp_number:=B1
End loop

In this case the inner query will be accessed by emp_number index and query will be faster.
If in this case there is a index SKIP scan on emp table then that means emp_number is not the leading column on the index.

I think it doesnt explain this:
do the indexes affect the performance of join queries? If so,how?
---i mean the indexes on columns of driving table and driven table.

suppose i have indices test1 on column d_id of table e and test2 on column d_id of table d..
Then how will the following query use indices test1 and test2 in any way?
select * from d,e where e.d_id=d.d_id;