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Examine the command：   ALTER DATABASE ADD SUPPLEMENTAL LOG DATA （PRIMARY KEY） COLUMNS；   What does the command accomplish？（）
A:Creates an additional copy of the database online redo log files. 
B:Stores the primary key column values of each row involved in a DML operation in the online redo log files. 
C:Stores the primary key column values of each row involved in a DML operation in the supplemental log files. 
D:Stores the old and new primary key column values of each row involved in a DML operation only when the primary key is modified in the online redo log files.

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出自：Oracle认证

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