如何使用函数覆盖

给大家展现一下这几件神剑神甲的属性：了解了傲视遮天神剑神甲的属性后 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_XTVAL, \'Scott\', \'Smith\', \'Computer Science\', 98,null);INSERT INTO students (id, first_name, last_name, major, current_credits,grade) VALUES (student_XTVAL, \'Margaret\', \'Mason\', \'History\', 88,null);INSERT INTO students (id, first_name, last_name, major, current_credits,grade) VALUES (student_XTVAL, \'Joanne\', \'Junebug\', \'Computer Science\', 75,null);INSERT INTO students (id, first_name, last_name, major, current_credits,grade) VALUES (student_XTVAL, \'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 studentsset 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 gradefrom students) awhere = )/

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

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