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Which three statements are true about SQL plan directives?（）
A:They are tied to a specific statement or SQL id.
B:They instruct the maintenance job to collect missing statistics or perform dynamic sampling to generate a more optimal plan.
C:They are used to gather only missing statistics.
D:They are created for a query expression where statistics are missing or the cardinality estimates by the optimizer are incorrect.
E:They instruct the optimizer to create only column group statistics.
F:Improve plan accuracy by persisting both compilation and execution statistics in the SYSAUX tablespace.

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出自：Oracle认证

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