-语法2: insert into tablename sub-query
--例子:
insert into emp_temp (select * from emp where deptno = 20)
--创建一个emp的临时复制表
create table emp_temp as select * from emp where 1 = 2
--delete关键字
--作用:删除表中的数据
--语法: delete [from] tablename [where condition]
--例子:
delete emp_temp where empno = 8888;
小心使用 delete emp_temp;
--update关键字
--作用:更新表中的数据
--语法: update tablename set column1=value1,column2=value2,...,columnN=valueN [where condition]
--例子:
update emp_temp set sal = sal*1.2 where ename = 'SMITH';
事务
--转账
update emp_temp set sal = sal - 500 where ename='JONES';
update emp_temp set sal = sal + 500 where ename='SMITH';
commit;
rollback;
create table aaa(id number,name varchar2(20));
insert into emp_temp(empno,ename) values(1111,'cai10');
insert into emp_temp(empno,ename) values(2222,'cai20');
--savepoint 存档点
savepoint sp1;
insert into emp_temp(empno,ename) values(3333,'cai30');
insert into emp_temp(empno,ename) values(4444,'cai40');
rollback to sp1;
--事务的四个特性:ACID
--原子性(A)
--一致性(C)
update emp_temp set sal = 5000 where empno=1111
update emp_temp set sal = sal+1000 where empno = 1111;
--隔离性(I)
--持久性(D)
用户管理
--1.创建一个账户
create user zhangsan identified by 123456;
--2.修改账户的密码
alter user zhangsan identified by 654321;
--3.删除一个账户 [cascade 表示是否级联删除]
--4.让一个用户的密码失效
alter user zhangsan password expire;
--5.锁定、解锁一个账户
alter user zhangsan account lock;
alter user zhangsan account unlock;
--DCL
--grant授予权限
--revoke收回权限
--1.给用户授权
--允许用户登录
grant create session to zhangsan;
--给账户授权可以操作表
grant all on scott.emp_temp to zhangsan;
--2.取消用户的权限
revoke all on scott.emp_temp from zhangsan;
--创建序列
create sequence seq_emp_temp
increment by 1
start with 1
--使用序列
--通过序列名.next_val
自增序列: select seq_emp_temp.nextval from dual;
查询序列: select seq_emp_temp.currval from dual;
使用一次加一行序列加一: insert into emp_temp(empno) values(seq_emp_temp.nextval)
视图
--登录到sys账户给scott赋予创建视图的权限: grant create view to scott;
--1.视图的创建
create view v$_emp_dept
as
select ename,sal,job,dname from emp,dept where emp.deptno = dept.deptno;
--视图也可以从视图中产生
create view v$_emp_dept_tem
as
select ename,sal from v$_emp_dept
--修改视图的数据,就是修改基表的数据
create or replace view v$_emp
as
select empno,ename from emp
with read only
select * from v$_emp;
select * from emp;
update emp set sal = 8888 where empno = 9527;
--视图的优点:可以使某些重复出现SQL语句变得更为简单
--视图的缺点:1.如果修改基表的结构,视图失效
-- 2.增加数据库的维护成本
-- 3.视图会被覆盖掉
-- 4.一般情况下,不要对视图进行DML操作
--视图的例子
select dname, grade
from (select deptno, avg_sal, grade from (select deptno, avg(sal) avg_sal from emp group by deptno) t, salgrade s where t.avg_sal between s.losal and s.hisal) t1,
dept
where t1.deptno = dept.deptno
and t1.grade =
(select min(grade)
from (select deptno, avg_sal, grade from (select deptno, avg(sal) avg_sal from emp group by deptno) t, salgrade s where t.avg_sal be