OCP-1Z0-051-V9.02-109题

109. Examine the structure of the MARKS table:

name Null Type

STUDENT_ID NOT NULL VARCHAR2(4)

STUDENT_NAME VARCHAR2(25)

SUBJECT1 NUMBER(3)

SUBJECT2 NUMBER(3)

SUBJECT3 NUMBER(3)

Which two statements would execute successfully? (Choose two.)

A. SELECT student_name,subject1

FROM marks

WHERE subject1 > ***G(subject1); where不能跟表达式

B. SELECT student_name,SUM(subject1)

FROM marks

WHERE student_name LIKE 'R%'; 少了group by

C. SELECT SUM(subject1+subject2+subject3)

FROM marks

WHERE student_name IS NULL;

D. SELECT SUM(DISTINCT NVL(subject1,0)), MAX(subject1)

FROM marks

WHERE subject1 > subject2;

Answer: CD



答案解析：

实验测试：

首先创建marks表

scott@TEST0924> create table marks
2 (student_id varchar2(4) not null,
3 student_name varchar(25),
4 subject1 number(3),
5 subject2 number(3),
6 subject3 number(3)
7 );

插入几条数据后查询如下：

scott@TEST0924> select * from marks;

STUD STUDENT_NAME SUBJECT1 SUBJECT2 SUBJECT3
---- ------------------------- ---------- ---------- ----------
1 aa 88 89 90
2 bb 85 85 80
3 cc 87 81 95


A答案：AGV分组函数不能用在where子句里

scott@TEST0924> SELECT student_name,subject1
2 FROM marks
3 WHERE subject1 > ***G(subject1);
WHERE subject1 > ***G(subject1)
*
ERROR at line 3:
ORA-00934: group function is not allowed here


scott@TEST0924> SELECT student_name,subject1
2 FROM marks
3 WHERE subject1>(select ***G(subject1) from marks);

STUDENT_NAME SUBJECT1
------------------------- ----------
aa 88
cc 87


B答案：缺少group by

scott@TEST0924> SELECT student_name,SUM(subject1)
2 FROM marks
3 WHERE student_name LIKE 'a%';
SELECT student_name,SUM(subject1)
*
ERROR at line 1:
ORA-00937: not a single-group group function


scott@TEST0924> SELECT student_name,SUM(subject1)
2 FROM marks
3 WHERE student_name LIKE 'a%'
4 group by student_name;

STUDENT_NAME SUM(SUBJECT1)
------------------------- -------------
aa 88


C答案：因为测试数据里没有student_name没有为空的，所有无返回值。

cott@TEST0924> SELECT SUM(subject1+subject2+subject3)
2 FROM marks
3 WHERE student_name IS NULL;

SUM(SUBJECT1+SUBJECT2+SUBJECT3)
-------------------------------

故用is not null 一样的测试效果。
scott@TEST0924>
scott@TEST0924> SELECT SUM(subject1+subject2+subject3)
2 FROM marks
3 WHERE student_name IS not NULL;

SUM(SUBJECT1+SUBJECT2+SUBJECT3)
-------------------------------
780

D答案：

cott@TEST0924> SELECT SUM(DISTINCT NVL(subject1,0)), MAX(subject1)
2 FROM marks
3 WHERE subject1 > subject2;

SUM(DISTINCTNVL(SUBJECT1,0)) MAX(SUBJECT1)
---------------------------- -------------
87 87