1.创建测试表:

复制代码 代码如下:

DROP SEQUENCE student_sequence;

CREATE SEQUENCE student_sequence START WITH 10000 INCREMENT BY 1;

DROP TABLE students;

CREATE TABLE students (

id NUMBER(5) PRIMARY KEY,

first_name VARCHAR2(20),

last_name VARCHAR2(20),

major VARCHAR2(30),

current_credits NUMBER(3),

grade varchar2(2));

INSERT INTO students (id, first_name, last_name, major, current_credits,grade)

VALUES (student_sequence.NEXTVAL, 'Scott', 'Smith', 'Computer Science', 98,null);

INSERT INTO students (id, first_name, last_name, major, current_credits,grade)

VALUES (student_sequence.NEXTVAL, 'Margaret', 'Mason', 'History', 88,null);

INSERT INTO students (id, first_name, last_name, major, current_credits,grade)

VALUES (student_sequence.NEXTVAL, 'Joanne', 'Junebug', 'Computer Science', 75,null);

INSERT INTO students (id, first_name, last_name, major, current_credits,grade)

VALUES (student_sequence.NEXTVAL, 'Manish', 'Murgratroid', 'Economics', 66,null);

commit;

2.查看相应数据

复制代码 代码如下:

SQL> select * from students;

ID FIRST_NAME LAST_NAME MAJOR CURRENT_CREDITS GR

---------- -------------------- -------------------- ------------------------------ --------------- --

10000 Scott Smith Computer Science 98

10001 Margaret Mason History 88

10002 Joanne Junebug Computer Science 75

10003 Manish Murgratroid Economics 66

3.更新语句

复制代码 代码如下:

update students

set grade = (

select grade from

(

select id,

case when current_credits > 90 then 'a'

when current_credits > 80 then 'b'

when current_credits > 70 then 'c'

else 'd' end grade

from students

) a

where a.id = students.id

)

/

4.更新后结果

复制代码 代码如下:

SQL> select * from students;

ID FIRST_NAME LAST_NAME MAJOR CURRENT_CREDITS GR

---------- -------------------- -------------------- ------------------------------ --------------- --

10000 Scott Smith Computer Science 98 a

10001 Margaret Mason History 88 b

10002 Joanne Junebug Computer Science 75 c

10003 Manish Murgratroid Economics 66 d