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047-064

原创 Linux操作系统 作者:jbymy2000 时间:2012-03-18 09:44:59 0 删除 编辑
64. Evaluate the following SELECT statement and view the Exhibit to examine
its output:
SELECT constraint_name, constraint_type, search_condition,
r_constraint_name, delete_rule, status
FROM user_constraints WHERE table_name = ORDERS
Which two statements are true about the output? (Choose two.)
A. In the second column, indicates a check constraint.
B. The STATUS column indicates whether the table is currently in use.
C. The R_CONSTRAINT_NAME column gives the alternative name for the
constraint.
D. The column DELETE_RULE decides the state of the related rows in the child
table when the corresponding row is deleted from the parent table.
Answer: AD
Indicates:指示 Alternative:选择
CONSTRAINT_NAME CONSTRAINT_TYPE R_CONSTRAINT_NAME STATUS
------------------------ --------------- ------------------ --------
PK_CRUISE P ENABLED
FK_CRUISES_CRUISE_TYPES R PK_CRUISE_TYPE_ID ENABLED
FK_CRUISES_SHIPS R PK_SHIP ENABLED
FK_CRUISES_EMPLOYEES R PK_EMPLOYEES ENABLED
constraint_type的值为 'R '的表示your table受到其它表的约束,即your table
是从表, r_constraint_name就是reference constraint name 外键约束的名字
选项D的意思是否是DELETE级联

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