Explanation:
To transfer the data from the external table to the dimension table as efficiently as possible you need to use the MERGE command. The MERGE command helps to retrieve rows from a source table and either update existing rows or insert new rows into a destination table. You update the row in the destination table if there is a matching row in the destination table; otherwise, you insert a new row into the destination table.
Incorrect Answers:
2: The SELECT … CROSS JOIN command can be used to create a Cartesian product.
3: The INSERT ALL ... SELECT command will not help you in this case.
4: The CREATE VIEW ... CONSTRAINT cannot be used for purpose to insert new records or to update existing records in the dimension table.
Reference:
OCP Oracle9i Database: New Features for Administrators, Daniel Benjamin, p. 253
Chapter 5: Language Enhancements
Oracle 9i New Features, Robert Freeman, p. 122-123
Chapter 4: New Oracle9i Database DSS and Data-Warehouse Features

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