21建立班级表
CREATE TABLE class( classId NUMBER(2), cName VARCHAR2(40)); insert into class values(001,'计算机科学与技术'); insert into class values(002,'计算机科学与技术'); insert into class values(003,'计算机科学与技术'); insert into class values(004,'计算机科学与技术'); insert into class values(005,'财务管理'); insert into class values(006,'财务管理'); insert into class values(007,'会计专业'); insert into class values(008,'会计专业');
22
alter table class add(name varchar(20)); UPDATE class SET name = '歌谣' WHERE classid = '1'; UPDATE class SET name = '歌谣' WHERE classid = '2'; UPDATE class SET name = '歌谣' WHERE classid = '3'; UPDATE class SET name = '歌谣' WHERE classid = '4'; UPDATE class SET name = '歌谣' WHERE classid = '5'; UPDATE class SET name = '歌谣' WHERE classid = '6'; UPDATE class SET name = '歌谣' WHERE classid = '7'; UPDATE class SET name = '歌谣' WHERE classid = '8';
23 select name from student union all select name from class;
--Union：对两个结果集进行并集操作，不包括重复行，同时进行默认规则的排序；
--Union All：对两个结果集进行并集操作，包括重复行，不进行排序；
24在两个表中查找共同行
create view E as select xh,sex,name from student where name='歌谣' select * from E
25从一个表中查找另一个表中没有的值
select name from student minus select name from class--查找class中没有的行
