本文探讨了数据库中索引的基本概念及其与表约束之间的关系。主要内容包括：当表被删除时，其对应的索引也会自动删除；每次进行数据操作时，相关索引会自动更新；非延迟的主键或唯一键约束将自动生成唯一索引。
Q55. Which statements are correct regarding indexes? (Choose all that apply.)
A. When a table is dropped, the corresponding indexes are automatically dropped.
B. For each DML operation performed, the corresponding indexes are automatically updated.
C. Indexes should be created on columns that are frequently referenced as part of any expression.
D. A non-deferrable PRIMARY KEY or UNIQUE KEY constraint in a table automatically creates a unique index.
Correct Answer: ABD
Explanation/Reference:
References:
http://viralpatel.net/blogs/understanding-primary-keypk-constraint-in-oracle/
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