E . True. Both & and && can prefix substitution variables in queries as well as in DML statements. & is used for defining a substitution variable that prompts the user every time the variable is encountered. && is used for a persistent substitution variable that, once defined in the session, will not prompt the user again for a value if used subsequently.

A . This statement is incorrect. An INVISIBLE index is maintained during DML operations just like a VISIBLE index. The difference is that an INVISIBLE index is not used by the optimizer unless explicitly hinted. B. This statement is correct. When creating a table, you can define indexes on one or more columns as part of the table definition. C. This statement is incorrect. While a DROP INDEX statement will drop the index, it does not always prevent updates to the table. If the index is marked as unusable or is an invisible index, for example, updates can still be performed. D. This statement is correct. It is possible to have both a UNIQUE index and a non-unique index on the same column. The UNIQUE index enforces the uniqueness of column values, while the non-unique index does not. E. This statement is correct to some extent. Descending indexes are not function-based indexes per se, but they are indexes on which the data is sorted in descending order, as opposed to the default ascending order. However, descending indexes are conceptually related to function-based indexes because they alter the way the indexed data is stored. F. This statement is incorrect. The use of an index in query execution depends on the optimizer's decision, which is based on statistics and the cost associated with using the index. There are situations where the optimizer may choose a full table scan even if there is an index on the filter column.

Reference can be found in the Oracle Database Concepts Guide and the SQL Language Reference documentation, which detail the behavior of indexes and how they are managed within the Oracle database.

External tables using the ORACLE_DATAPUMP access driver have specific characteristics:

C . Creating an external table using the ORACLE_DATAPUMP access driver allows you to select data from other tables, including another external table or a regular table whose rows are stored in database blocks.

A, B, D, and E are incorrect. Specifically:

A is incorrect because creating an external table does not automatically create a directory object; the directory object must exist prior to or be created separately.

B is incorrect as it limits the creation to tables stored in database blocks, which is not a restriction.

D is incorrect because creating an external table does not create a dump file; it reads from an existing dump file created by Data Pump.

E is also incorrect because the dump file is not created as part of the external table creation process.

Oracle Database SQL Language Reference, 12c Release 1 (12.1): 'CREATE TABLE' for External Tables

When comparing the performance of different SQL join types and conditions, Oracle SQL optimizations generally ensure that performance is consistent across different syntactical forms of expressing the same logic:

Option A: False. The BETWEEN condition does not inherently perform worse than using >= and <=. Oracle's optimizer typically evaluates these conditions similarly, optimizing the underlying execution based on the data distribution and available indexes.

Option B: False. Oracle's optimizer is designed to handle both Oracle-specific join syntax and ANSI join syntax with equal competence. Performance differences would typically be negligible because the optimizer translates both into an optimal execution plan based on the same underlying mechanisms.

Option C: True. The join syntax used (whether Oracle's traditional syntax or ANSI standard syntax) generally does not affect the performance. Oracle's query optimizer is adept at translating different syntaxes into efficient execution plans.

Option D: False. The assertion that BETWEEN always performs better than >= and <= is incorrect. Performance depends more on factors like indexing, the specific data and distribution, and the Oracle optimizer's capabilities than on the mere choice of syntax.

Option E: False. While table aliases help improve query readability and can prevent ambiguity in SQL queries, they do not inherently improve performance. Their use is a best practice for code clarity and maintenance, not performance enhancement.

The WITH GRANT OPTION clause in Oracle SQL allows the grantee to grant the privilege they have received to another user or role.

E . It cannot be used to pass on privileges to PUBLIC by the grantee: The WITH GRANT OPTION does not allow the grantee to pass on privileges to PUBLIC. Only the object's owner or a user with the GRANT ANY OBJECT PRIVILEGE system privilege can grant privileges to PUBLIC.

F . It can be used to pass on privileges to other users by the grantee: This is true. When a user receives privileges with the WITH GRANT OPTION, they can grant that privilege to another user or role.

Oracle Database SQL Language Reference 12c, specifically sections on user privileges and the WITH GRANT OPTION.