Oracle基础

--创建表students

create table students(

studentsid number(10) primary key,

sname varchar2(10) not null,

sex varchar2(4),

grade number(3),

classid number(10),foreign key (classid) references class(classid)

);

--重命名表students中字段studentsid

alter table students rename column studentsid to studentid;

--在表students中添加字段

alter table students add

studentid number(8) primary key;

--在表students中删除字段studentsid

alter table students drop (studentsid);

--删除表students

drop table students;

--创建表class

create table class (

classid number(10),

cname varchar2(20)

)

--修改表class中字段classid为主键

alter table class modify (classid number(10) primary key);

alter table students modify (studentid number(10));

--创建视图ST

create view ST as

select sname,sex from students;

--删除视图ST

drop view ST;

--创建视图SDetail,students详细信息

create view SDetail as

select s.studentid,s.sname,s.sex,s.grade,c.cname from students s,class c;

--在表students中插入数据

insert into students(studentid,sname,sex,grade,classid) values(10001,'Jim','男',65,1001)

insert into class (classid,cname) values(1001,'信息与技术科学')

--删除表中数据

delete from students t where t.studentid=10001; 

--更新表中id

update students set studentid=rownum+10000;

--插入新的id的数据，但只能一条条插入

insert into students (studentid,sname)

select distinct a.m,students.sname from students,(select max(studentid)+1 m from students) a

--插入数据，多条，推荐，可多次使用
declare

 i number(2);

 begin

   for i in 1..8 loop

      insert into students (studentid,sname)

      select distinct a.m,students.sname from students,(select max(studentid)+1 m from students) a;

   end loop;

   end;

   

   

--插入studentid为random类型的。控制id五位数,只能插入一条，且插入的id格式不一致

insert into students (studentid,sname)

select substr(cast(dbms_random.value as varchar2(1000)),5,5),students.sname from dual,students;

select count(*) from students

练习：

--首字母最大，结果为Hello World

select initcap('hello world') from dual

---创建比赛记录表，mdate日期，rq胜负
create table Match(
mdate date,
rq varchar2(4)
);

--插入数据
insert into match values('2005-5-10','胜')

---------------------------------------------------------------------
--用于归纳不同分类时用，此例为归纳每个月胜或负的总数
--方法1：用case...when...then...else...语句
select mdate,sum(case when rq='胜' then 1 else 0 end) as 胜,sum(case when rq='负' then 1 else 0 end) as 负 from match
group by mdate
--方法2：用嵌套子查询+where
select a.mdate,a.胜,b.负 from
(select mdate,count(rq) 胜 from match where rq='胜' group by mdate) a,
(select mdate,count(rq) 负 from match where rq='负'group by mdate) b
where a.mdate=b.mdate
--方法3：用嵌套子查询+join on
select a.mdate,a.胜,b.负 from
(select mdate,count(rq) 胜 from match where rq='胜' group by mdate) a join
(select mdate,count(rq) 负 from match where rq='负'group by mdate) b
on a.mdate=b.mdate
-----------------------------------------------------------------------------------
--日期格式做对比，必须使用to_char进行转换，否则对比没有返回结果
select * from se_innerapplies t where to_char(t.operatedate,'yyyy-mm-dd')=to_char(sysdate,'yyyy-mm-dd')

-----查询
--结果显示为
create table Score(
scoreid varchar2(10) primary key,
studentid varchar2(10),
mark number(3),
subject varchar(20)
)

----查询每个学生每门课程是否及格。使用case...when...then...when...then...else...end
select d.studentid,(case when d.mark>=80 then '优秀' when d.mark>60  then '及格' else '不及格' end) , d.subject
from score d
---- 右连接
select d.studentid,d.subject from score d right join (select studentid,mark from score) f
on d.studentid=f.studentid
----查询每个学生有多少成绩记录
select d.studentid,count(*) as 总数 from score d group by d.studentid having count(*)>1