Create B-tree Index in Oracle

CREATE [UNIQUE] INDEX maxamount ON
Sales(amount)
TABLESPACE tab_space;

where
UNIQUE means that the values in the indexed columns must be unique.
index_name is the name of the index.
table_name is a database table.
column_name is the indexed column. You can create an index on multiple columns
(these kind of  index is known as a composite index).
tab_space is the tablespace for the index. If you don’t provide a tablespace, the index
is stored in the user’s default tablespace.

Note:
For performance reasons, you should typically store indexes in a
different tablespace from tables.