史上最强的oracle数据库面试题

oracle Certification Program (OCP认证)的题目

　　(1) A 表中有100条记录.

　　Select　* FROM A Where A.COLUMN1 = A.COLUMN1

　　这个语句返回几条记录? (简单吧,似乎1秒钟就有答案了:)

　　(2) Create SEQUENCE PEAK_NO

　　Select PEAK_NO.NEXTVAL FROM DUAL --> 假设返回1

　　10秒中后,再次做


　　Select PEAK_NO.NEXTVAL FROM DUAL --> 返回多少?

　　(3) SQL> connect sys as sysdba

　　Connected.


　　SQL> insert into dual values ( 'Y');

　　　　　1 row created.

　　SQL> commit;

　　　　　Commit complete.

　　SQL> select count(*) from dual;

　　　　　COUNT(*)

　　　　　----------

　　　　　2

　　SQL> delete from dual;

　　　　　commit;

　　　　　-->DUAL里还剩几条记录?

　　JUST TRY IT
一些高难度的SQL面试题

  以下的null代表真的null，写在这里只是为了让大家看清楚


根据如下表的查询结果，那么以下语句的结果是（知识点：not in/not exists+null）
SQL> select * from usertable;
USERID           USERNAME
-----------      ----------------
     1          user1
     2          null
     3          user3
     4          null
     5          user5
     6          user6
      
SQL> select * from usergrade;
USERID         USERNAME           GRADE
----------     ----------------   ----------
     1        user1              90
     2        null               80
     7        user7              80
     8        user8              90
执行语句：

select count(*) from usergrade where username not in (select username from usertable);

select count(*) from usergrade g where not exists
(select null from usertable t where t.userid=g.userid and t.username=g.username);

结果为：语句1(  0 )   语句2  (  3 )

A: 0     B:1     C:2     D:3      E:NULL


2

在以下的表的显示结果中，以下语句的执行结果是（知识点：in/exists+rownum）
SQL> select * from usertable;
USERID           USERNAME
-----------      ----------------
     1          user1
     2          user2
     3          user3
     4          user4
     5          user5
      
SQL> select * from usergrade;
USERNAME               GRADE
----------------       ----------
user9                  90
user8                  80
user7                  80
user2                  90
user1                  100
user1                  80

执行语句
Select count(*) from usertable t1 where username in
  (select username from usergrade t2 where rownum <=1);
  
Select count(*) from usertable t1 where exists
  (select 'x' from usergrade t2 where t1.username=t2.username and rownum <=1);

以上语句的执行结果是：(  )  (  )
  A:   0        B:   1        C:   2       D:  3

根据以下的在不同会话与时间点的操作，判断结果是多少，其中时间T1原始表记录为；
select * from emp;
EMPNO         DEPTNO       SALARY
-----         ------       ------
100            1           55
101            1           50

select * from dept;
DEPTNO           SUM_OF_SALARY
------           -------------
1                105
2                

可以看到，现在因为还没有部门2的员工，所以总薪水为null，现在，
有两个不同的用户（会话）在不同的时间点（按照特定的时间顺序）执行了一系列的操作，那么在其中或最后的结果为：

time              session 1                            session2
-----------      -------------------------------       -----------------------------------
T1               insert into emp
                 values(102,2,60)
                  
T2                                                     update emp set deptno =2
                                                        where empno=100

T3                                                    update dept set sum_of_salary =
                                                       (select sum(salary) from emp
                                                     where emp.deptno=dept.deptno)
                                                     where dept.deptno in(1,2);
                                                  
T4           update dept set sum_of_salary =
                (select sum(salary) from emp
            where emp.deptno=dept.deptno)
            where dept.deptno in(1,2);
              
T5                                                    commit;

T6                                                    select sum(salary) from emp group by deptno;
                                                     问题一：这里会话2的查询结果为：                                                  
T7          commit;
=======到这里为此，所有事务都已完成，所以以下查询与会话已没有关系========

T8          select sum(salary) from emp group by deptno;
            问题二：这里查询结果为

T9         select * from dept;
            问题三：这里查询的结果为

问题一的结果(  )  问题二的结果是(  )  问题三的结果是(  )

A:                        B:
----------------         ----------------
1        50               1        50
2        60               2        55

C:                        D:
----------------         ----------------
1        50               1       115
2       115               2        50

E:                        F:
----------------         ----------------
1       105               1       110
2        60               2        55


有表一的查询结果如下，该表为学生成绩表（知识点：关联更新）
select id,grade from student_grade
ID                 GRADE
--------           -----------
1                  50
2                  40
3                  70
4                  80
5                  30
6                  90

表二为补考成绩表
select id,grade from student_makeup
ID                 GRADE
--------           -----------
1                  60
2                  80
5                  60

现在有一个dba通过如下语句把补考成绩更新到成绩表中，并提交：
update student_grade s set s.grade =
(select t.grade from student_makeup t
   where s.id=t.id);
commit;
请问之后查询：
select GRADE from student_grade where id = 3;结果为：

A: 0    B:  70   C:  null   D:  以上都不对


根据以下的在不同会话与时间点的操作，判断结果是多少，
其中时间T1
                session1                              session2
--------------------------------------     ----------------------------------------
T1         select count(*) from t;
          --显示结果(1000)条
          
T2         delete from t where rownum <=100;

T3                                          begin
                                             delete from t where rownum <=100;  
                                             commit;
                                           end;
                                           /
                                              
T4         truncate table t;

T5         select count(*) from t;
          --这里显示的结果是多少

A:  1000        B:   900     C:   800     D:   0