Oracle HowTo:如何使用Oracle case函数

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_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