169. You have two tables with referential integrity enforced between them. You need to insert data to the
child table first because it is going to be a long transaction and data for the parent table will be available in
a later stage, which can be inserted as part of the same transaction.
View the Exhibit to examine the commands used to create tables.
Which action would you take to delay the referential integrity checking until the end of the transaction?
A.Set the constraint to deferred before starting the transaction.
B.Alter the constraint to NOVALIDATE state before starting the transaction.
C.Enable the resumable mode for the session before starting the transaction.
D.Set the COMMIT_WAIT parameter to FORCE_WAIT for the session before starting the transaction.
Answer: A
答案解析：
参考：http://docs.oracle.com/cd/E11882_01/server.112/e41084/statements_10003.htm#SQLRF55408
你有两个表，它们之间有参照完整性的约束。在同一个事务中，你需要先在子表中插入数据，然后再使父表变为可用。
从图上可知，orders表是子表，它的item_code列参照items表的iitem_code，但是题中是先在子表中插入数据，然后再让父表变为可用，在有外键约束的情况下，这样是不能插入的，所以，可以在执行事务前，设置约束延迟生效，即在事务提交时生效，即可。
Specify DEFERRED to indicate that the conditions specified by the deferrable constraint are checked when the transaction is committed.
The following statement checks three deferred constraints when the transaction is committed. This example fails if the constraints were specified to be NOTDEFERRABLE.