You create a table with the PERIOD FOR clause to enable the use of the Temporal Validity feature of Oracle Database 12c. Examine the table definition: create table employees (empno number, salary…

Question

Options

• AThe valid time columns employee_time_start and employee_time_end are automatically
• BThesamestatementmayfilteronbothtransactiontimeandvalidtemporaltimebyusingthe AS OF
• CThe valid time columns are not populated by the Oracle Server automatically.
• DThe valid time columns are visible by default when the table is described.
• ESetting the session valid time using

• A
  72% (23)
• D
  9% (3)
• E
  19% (6)

Explanation

When you define PERIOD FOR employee_time, Oracle automatically creates two hidden columns - employee_time_start and employee_time_end - making A correct. However, Oracle only creates the columns; it never populates them with data, so the application must set start/end values explicitly, making C correct. Oracle 12c also allows a single SQL statement to combine Flashback (transaction time) via AS OF SCN/TIMESTAMP with valid-time filtering via AS OF PERIOD FOR, making B correct.

D is wrong because the auto-created period columns are hidden - a standard DESCRIBE does not show them; you must query USER_TAB_COLS with HIDDEN_COLUMN = 'YES' to find them. E is wrong (or incomplete) because setting session-level valid time via DBMS_FLASHBACK_ARCHIVE.ENABLE_AT_VALID_TIME applies a filter globally to the session, which is a valid technique but is not done with the AS OF clause - it's a separate mechanism, so conflating the two makes the statement false as written.

Memory tip: Think of PERIOD FOR as Oracle building you an empty picture frame (it creates the columns) but leaving you to hang the picture yourself (you populate the dates). The AS OF keyword is your "time telescope" - powerful enough to look through two lenses (transaction time + valid time) at once.

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