Question 5
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Question:
A constraint in a table is defined with the INITIALLY IMMEDIATE clause. You executed the ALTER TABLE command with the ENABLE VALIDATE option to enable the constraint that was disabled.
What are the two effects of this command? (Choose two.)
A) It fails if any existing row violates the constraint.
B) It does not validate the existing data in the table.
C) It enables the constraint to be enforced at the end of each transaction.
D) It prevents insert, update, and delete operations on the table while the constraint is in the process of being enabled.
Answer:A,D
Translate:
在表中定义了一个含有
INITIALLY IMMEDIATE子句的约束。你执行了带有ENABLE VALIDATE 选项的ALTER TABLE命令来开启约束。
这条命令的两个影响是什么?
A.如果有任意存在违反约束的行,则会失败。
B.不会使表中存在的数据生效。
C.会在每一个事务的结尾是约束强制执行。
D.当约束正在开启的过程中,会阻止insert,update和delete操作。
Notes:
Enable validate 要求新旧数据必须同时满足约束规则-在规则正在进行中时是不容许在表上进行任何DML操作的
Enable novalidate 已存在数据可以不满足,但是新数据必须满足
Disable validate 不容许在表上进行任何DML操作,对主键和唯一约束来说,会删除相应的唯一索引,但约束规则仍然有效
Disable novalidate数据不满足约束规则,对主键和唯一约束来说,会删除相应的唯一索引
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