Explanation:
Indexes are created automatically by Oracle to support integrity constraints that enforce uniqueness. The two types of integrity constraints that enforce uniqueness are PRIMARY KEY and UNIQUE constraints. When the primary key or UNIQUE constraint is declared, a unique index to support the column’s uniqueness is also created, and all values in all columns that were defined as part of the primary key or UNIQUE constraint are placed into the index.
Incorrect Answers:
2: There will not be index for ORDER_ID column.
3: There will not be index for STATUS column.
4: There will not be index for PROD_ID column.
5: There will not be index for ORD_TOTAL column.
OCP Introduction to Oracle 9i: SQL Exam Guide, Jason Couchman, p. 237-238
Chapter 5: Creating Oracle Database Objects

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