Which two statements are true about indexes and their administration in an Oracle database?

Question

Options

• AAn index can be scanned to satisfy a query without the indexed table being accessed.
• BA non-unique index can be converted to a unique index using a Data Definition Language (DDL)
• CA descending index is a type of bitmapped index.
• DAn invisible index is maintained when a Data Manipulation Language (DML) command is per-
• EAn index is always created by scanning the key columns from the underlying table.

• A
  76% (25)
• B
  3% (1)
• C
  6% (2)
• E
  15% (5)

Explanation

Option A is correct because Oracle supports index-only scans (also called covering index access): if every column a query needs is stored in the index, Oracle reads only the index and never touches the base table - a significant performance advantage.

Option D is correct because an invisible index is hidden from the query optimizer (it won't be used in execution plans by default), but Oracle still maintains it during all DML operations (INSERT, UPDATE, DELETE). This lets DBAs test an index's viability before exposing it to the optimizer.

Why the distractors are wrong:

• B - You cannot alter a non-unique index into a unique index with a single DDL command; you must drop and recreate it (or add a UNIQUE constraint).
• C - A descending index is a B-tree index with keys stored in reverse order, not a bitmap index; these are entirely different index types.
• E - The word "always" makes this false: when using ALTER INDEX REBUILD, Oracle can reconstruct the index from the existing index structure rather than rescanning the table's key columns.

Memory tip: Think of invisible indexes as stealth mode - they stay active and up-to-date behind the scenes (D), just like an index-only scan works quietly behind the scenes without touching the table (A). Both are about index behavior that happens "under the hood."

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