通过实例简要介绍case函数的用法。
1.创建测试表:
DROP SEQUENCE student_sequence;
CREATE SEQUENCE student_sequenceSTART WITH 10000INCREMENT BY 1;
DROP TABLE students;
CREATE TABLE students (
id NUMBER(5) PRIMARY KEY,
first_name VARCHAR2(20),
last_nameVARCHAR2(20),
majorVARCHAR2(30),
current_creditsNUMBER(3),
gradevarchar2(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
SQL> select * from students;
ID FIRST_NAMELAST_NAMEMAJOR CURRENT_CREDITS GR
------ ----------------- ------------------- ----------- ----------------- -----
10000ScottSmithComputer Science 98
10001Margaret MasonHistory88
10002Joanne JunebugComputer Science 75
10003ManishMurgratroid Economics66
3.更新语句
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
SQL> select * from students;
ID FIRST_NAME LAST_NAMEMAJOR CURRENT_CREDITS GR
----------------------------- -------------------- ---------------------------- ----
10000 Scott SmithComputer Science98 a
10001 MargaretMasonHistory 88 b
10002 JoanneJunebugComputer Science75 c
10003 ManishMurgratroidEconomics 66 d
