Oracle之索引，視圖，序列綜合

--授予scott用戶dba權限
grant dba to scott;

select * from emp;
select * from dept;
select * from salgrade;

select * from user_indexes;

--自動創建索引
alter table emp add constraint un_ename unique(ename);

--刪除約束
alter table emp drop constraint un_ename;


/*
   手動創建索引
   create index 索引名 on 表名(列名1，列名2)
*/
create table bigtable(
   ename varchar2(20),
   address varchar2(30)
);

select * from bigtable;

--插入5000000條數據
declare 
begin 
  for i in 1..5000000 loop
    insert into bigtable values('姓名'||i,'地址'||i);
  end loop;
end;

select count(ename) from bigtable;

--沒有索引的情況下  查詢name='姓名3000000'的時間
select * from bigtable where ename='姓名3000000';

--創建索引
create index index_name on bigtable (ename) ;
select * from bigtable where ename= '姓名3000000' ;    --效率明顯增加很多
--創建複合索引
create index index_bigtable on bigtable (ename, address) ;
select * from bigtable where ename='姓名3000000' and address='地址3000000' ;

--.剛除索引
drop index index_bigtable;
drop index index_name;

--刪除表
drop table bigtable;
select * from tab;



/**
創建視圖
   CREATE [ot replace] view viewname
   [(列名)]
   as subquery
   [with read only]
*/

--HR經理視圖
create view HR_view 
as 
select * from emp;
select * from HR_VIEW;
--項目經理視圖
create view MGR_VIEW
as
select empno, ename from emp;
select * from mgr_view;

--刪除視圖
drop view mgr_view;

--查詢所有員工的基本信息，部門信息
create or replace view emp_view
as 
select e.empno,e.ename,e.job,e.mgr,e.hiredate,e.sal,e.comm,e.deptno,d.dname,d.loc
from emp e,dept d 
where e.deptno=d.deptno;

select * from emp_view;


--查詢所有員工的基本信息，年薪，年收入，部門信息
create or replace view emp_view
as 
select e.empno,e.ename,e.job,e.mgr,e.hiredate,e.sal,(e.sal*12) as "年薪",
(e.sal*12+nvl(e.comm, 0)) as "年輸入",e.comm,e.deptno,d.dname,d.loc
from emp e,dept d 
where e.deptno=d.deptno;


--統計每個部門的薪水，最高工資，最低工資，平均工資
create or replace view v_emp_sal
as
select deptno,
max(sal) as "最高工資"，
min(sal) as "最低工資"，
avg(sal) as "平均工資"
from emp
group by deptno;

select * from v_emp_sal;


/**
序列
  CREATE SEQUENCE序列名字
  START WITH序列初始值
  INCREMENT BY每次增長步長
  MAXVALUE最大值|NOMAXVALUE
  MINVALUE最小值|NOMINVALUE
  CYCLE|NOCYCLE|是否循環
  CACHE緩存的數量|NOCACHE

*/

--創建一-個循環序列
CREATE SEQUENCE seq_test1
START WITH 1
INCREMENT BY 2
MAXVALUE 30
CYCLE
CACHE 10;

--查詢序列
select * from user_sequences;


--序列取值
select seq_test1.currval from dual;
--必須執行一次nextval才能產生
select seq_test1.nextval from dual;

--常用序列
create sequence seq_test2;
select seq_test2.nextval from dual;

--使用序列實現表的id自增長
create sequence seq_test4;
create table test2(
  tid number primary key,
  tname varchar2(20)
);

--將序列運用到test2表中
insert into test2 values(seq_test4.nextval,'cici');
select * from test2;

delete from test2 where tid=4;