本文探讨了Oracle数据库中Optimizer统计特性的两个关键点：精确计算（B选项）与估算（E选项）。深入理解这些特性有助于数据库管理员和开发人员更有效地管理和优化查询性能。
Which two are true about Oracle's Optimizer statistics?
A)They are automatically updated when ddl statements execute.
B)They can be calculated exactly.
C)They can be gathered on external tables.
D)They are automatically updated when dml statements execute.
E)They can be estimated.
Answer: BE
赵：
estimated adj. 估计的;预计的;估算的;
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