USER1.EMP has a referential integrity constraint defined on EMP.DNO that references USER1.DEPT.DNO.

　　USER1 executes these commands:

　　SQL> UPDATE dept SET loc='UK' where dno=1;

　　1 row updated.

　　SQL> UPDATE emp SET sal=1000 where eno=100;

　　1 row updated.

　　SQL>ALTER TABLE dept DROP(dno)

　　What will be the outcome and why?

　　A)It will fail because a referential integrity constraint is defined on USER1.EMP.

　　B)It will execute successfully and drop DEPT.DNO.

　　C)It will fail because there is an uncommitted transaction on USER1.DEPT.

　　D)It will execute successfully and drop the DEPT.DNO and EMP.DNO columns.

　　E)It will fail because there is an uncommitted transaction on USER1.EMP

　　Answer: A

　　赵：

　　A 译：它将失败，因为 USER1.EMP 上定义了引用完整性约束。

　　×××：外键约束中，一个被作为外键引用的主键值不能直接删除，更不用说整个列