168.You execute this command to drop the ITEM table, which has the primary key referred in the ORDER
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168.You execute this command to drop the ITEM table, which has the primary key referred in the ORDER
table:
SQL> DROP TABLE scott.item CASCADE CONSTRAINTS PURGE;
Which two statements are true about the effect of the command? (Choose two.)
A.No flashback is possible to bring back the ITEM table.
B.The ORDER table is dropped along with the ITEM table.
C.The dependent referential integrity constraints in the ORDER table are disabled.
D.The dependent referential integrity constraints in the ORDER table are removed.The table definition of the ITEM table and associated indexes are placed in the
recycle bin.
答案:AD
解析:
CASCADE CONSTRAINTS 对应的索引会删除 D正确
purge 不会放入回收站,因此flashbak table不起作用A正确
B错误,如果想实现这个需要级联删除,
alter table order_status2 add constraint order_status2_modified_by_fk modified_by references
employees(employee_id) on delete cascade;
--使用了on delete cascade语句,用于删除父表一条记录的时候,子表记录也要删除
alter table order_status2 add constraint order_status2_modified_by_fk modified_by references
employees(employee_id) on delete set null;
--这里使用了on delete set null语句,当父表删除的时候,子表记录就会设置为空
table:
SQL> DROP TABLE scott.item CASCADE CONSTRAINTS PURGE;
Which two statements are true about the effect of the command? (Choose two.)
A.No flashback is possible to bring back the ITEM table.
B.The ORDER table is dropped along with the ITEM table.
C.The dependent referential integrity constraints in the ORDER table are disabled.
D.The dependent referential integrity constraints in the ORDER table are removed.The table definition of the ITEM table and associated indexes are placed in the
recycle bin.
答案:AD
解析:
CASCADE CONSTRAINTS 对应的索引会删除 D正确
purge 不会放入回收站,因此flashbak table不起作用A正确
B错误,如果想实现这个需要级联删除,
alter table order_status2 add constraint order_status2_modified_by_fk modified_by references
employees(employee_id) on delete cascade;
--使用了on delete cascade语句,用于删除父表一条记录的时候,子表记录也要删除
alter table order_status2 add constraint order_status2_modified_by_fk modified_by references
employees(employee_id) on delete set null;
--这里使用了on delete set null语句,当父表删除的时候,子表记录就会设置为空
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