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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: Which three statements are true concerning the use of the Valid Time Temporal feature for the EMPLOYEES table?（）
A:The valid time columns employee_time_start and employee_time_end are automatically created.
B:The same statement may filter on both transaction time and valid temporal time by using the AS OF TIMESTAMP and PERIOD FOR clauses.
C:The valid time columns are not populated by the Oracle Server automatically.
D:The valid time columns are visible by default when the table is described.
E:Setting the session valid time using DBMS_FLASHBACK_ARCHIVE.ENABLE_AT_VALID_TIME sets the visibility for data manipulatio

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出自：Oracle认证

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