Compund index vs simple index

Question

I want to know the differece between a compund index and a simple one.
For example I have a compund index with three fileds: field1, field2, field3
index type 1:
create index index1 on table1 (field1, field2, field3);
What happen if I change this compund index for a simple one?, something like this:
index type 2:
create index index1 on table1 (field1);
create index index2 on table1 (field2);
create index index3 on table1 (field3);
I think that index type 2 (simples one) takes more space than index type 1, isn't it???
I think index type 1 is more effective in a sql with all the indexed fields in the where, something like that: select * from table1 where field1 = ' ' and field2 = ' ' and field3 = ' ', but in any other sql is more effective index type 2 , isn't it???
is that true??, any other difference?
Any advice or design criteria about indexes (compund or simple) will be greatly appreciatted.
Thanks in advance

Answer 1

In my opinion most important thing between two is first has one index and the other has three :) Indexes result more I/O activity on update, insert and delete operations on the related table. So they need to be choosen carefully if you are creating them over heavily loaded oltp tables.
Also according to your query's where clause first index will be more selective, effective but this needs to be tested.