Oracle case函数使用介绍

三叶草

1.创建测试表:

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

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

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_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