Q: 96 Which three statements correctly describe the functions and use of
constraints? (Choose three.)
A. Constraints provide data independence.
B. Constraints make complex queries easy.
C. Constraints enforce rules at the view level.
D. Constraints enforce rules at the table level.
E. Constraints prevent the deletion of a table if there are dependencies.
F. Constraints prevent the deletion of an index if there are dependencies.
Answer: C, D, E
这道题目为什么选C、D、E呢，我觉得C不对，A对啊！
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注意 independence和dependencies的区别。
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C. 表上面如果有约束，基于此表的视图一样会有这个约束
是这样吗？
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SQL> create view v1 as select * from emp;
View created.
SQL> insert into v1 (empno) values (7900);
insert into v1 (empno) values (7900)
*
ERROR at line 1:
ORA-00001: unique constraint (SCOTT.PK_EMP) violated
SQL> insert into v1 (empno) values (9999);
1 row created.
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a是说约束保证了数据的独立性。
这不正与约束的作用相反吗。比如外键约束是反映了数据间的依存关系，与独立性正相反。