Oracle Database Discussions

Hello everyone,
i have one table about 20 000 000 rows, some developers have to generate reports on it and i want to create indexes on this table.
The table has 34 columns, no primary key, no unique keys.
The "where..." clause of the reports usually use 8 columns but some reports uses 8 + some other columns.
can any one help me on what kind of indexes do i have to create?
1. one index for each column used in "where clause"
2. one index for 8 columns and some other indexes for other used columns
3. one index for all columns
or something else etc...

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