index multiple or one by one columns?

[Zhiliang Hu]

Comparing between (1):

INDEX myindex (column_one, column_two, column_tthree)

and (2):

INDEX myindex1 (column_one),
INDEX myindex2 (column_two),
INDEX myindex3 (column_tthree)

What differences are there as how do they work? Does (1) becomes inefficient when you only search for "column_one" OR "column_two"? (since it has ONE index as reppresented by its index name).

Thanks!

Zhiliang