本例使用oracle数据库，使用PL/SQL可视化工具：
--查询员工表数据 （emp为pl/sql自带的表，也可自己新建）
select * from emp;
--创建表空间
create tablespace sp_java1608
datafile \'e:\data\data1.mdf\' size 100 M;
--修改表空间
--空间变为200M
alter tablespace sp_java1608
add datafile \'e:\data\data2.mdf\' size 100 M;
--删除表空间
drop tablespace sp_java1608 including contents and datafiles;
--创建用户（create user username identified by password）设置默认表空间
create user java1608
identified by java1608
default tablespace sp_java1608;
--删除用户
drop user java1608;
--赋予权限:
--connect :可以登录Oracle，不可以创建实体，不可以创建数据库结构。
--session 创建会话的权限
--DBA:拥有全部特权
--RESOURCE:拥有Resource权限的用户只可以创建实体，不可以创建数据库结构
grant create session to java1608;
grant create connect to Java1608;
grant resource to java1608;
--回收权限
revoke resource from java1608;
--rowID,rownum 都是伪列
--rowid在数据库中具有唯一性，在同一个数据库中是不会重复的，而rownum则可以理解为行号。
--常用于数据库分页
--如下例子：3当前是第几页,2代表每页显示几条数据
select * from
(
select rownum as eid,emp.* from emp
) tmp where eid between (3*2)+1 and (3+1)*2;
--单表查询
--select 列名1,列名2,... from 表名 where 条件
select * from emp;
select ename,sal from emp;
select * from emp where empno = 7369;
--distinct 除去列名重复
select distinct job from emp;
--oracle默认是隐式事务
--插入数据
insert into emp values(1000,\'张三\',\'CLERK\',7698,to_date(\'2000/01/01\',\'yyyy/mm/dd\'),300.5,100.6,20);
insert into emp values(1001,\'lisi\',\'CLERK\',7698,to_date(\'2000/01/01\',\'yyyy/mm/dd\'),300.5,100.6,20);
--rollback为撤回行为 与之相对的为commit提交事务
rollback;
--计算列
select ename,sal+comm as totalsal from emp where comm is not null;
select * from emp where ename like \'%E%\';
select * from emp where ename like \'%E_\';-- _伟%
--连接运算符
--dual 是为了让查询语法完成而存在的关键字
select \'a\' || \'b\' from dual;
--聚合函数，数据库通用函数
select min(sal) from emp;
select job, max(sal) from emp group by job having max(sal)>=2000;
select avg(sal) from emp;
select sum(sal) from emp;
select count(*) from emp;
--创建表
create table t_student
(
sno char(10),
name nvarchar2(6),
sex char(1),
address varchar2(200),
birthday date
);
select * from t_student;
insert into t_student(sex) values(\'m\');
--数据完成整性
--修改表/增加列
alter table t_student
add mphone char(11);
--修改表/修改列
alter table t_student
modify mphone char(12) not null;
--修改表/删除列
alter table t_student
drop column mphone;
--表改名
alter table t_student_1
rename to t_student;
--删除表
drop table t_student;
--实体完整性\域完整性\引用完整性(约束来实现)
--主键约束(非空,唯一,聚焦索引)
alter table t_student
add constraint pk_student_sno primary key (sno);
--非空约束
alter table t_student
modify name varchar2(6) not null;
alter table t_student
modify sex not null;
--默认值约束
alter table t_student
modify sex default \'m\';
--唯一性约束
alter table t_student
add constraint un_student_name unique (name);
--检查性约束
--between为前后闭区间
alter table t_student
add constraint ck_student_sex check (sex=\'m\' or sex =\'f\');
alter table t_student
add constraint ck_student_birthday check (birthday between to_date(\'1900/01/01\',\'yyyy/mm/dd\') and to_date(\'2016/11/27\',\'yyyy/mm/dd\'));
--外键约束
--主键（主表）；外键 (从表)
alter table t_score
add constraint fk_score_sno foreign key (sno) references t_student(sno);
create table t_score
(
sid int primary key,
math int not null,
chenese int not null,
sno char(10)
) ;
select * from t_score;
--删除表所有数据
delete from t_score;
--关联表数据一一对应
insert into t_score values(1,20,30,\'s001\');
insert into t_score values(2,20,30,\'s002\');
insert into t_score values(3,20,30,\'s003\');
insert into t_score values(4,20,30,\'s004\');
insert into t_student(sno,name,sex,birthday) values(\'s001\',\'zhang\',\'f\',to_date(\'1900/01/01\',\'YYYY/MM/DD\'));
insert into t_student(sno,name,sex,birthday) values(\'s002\',\'li\',\'m\',to_date(\'1900/01/01\',\'YYYY/MM/DD\'));
insert into t_student(sno,name,sex,birthday) values(\'s003\',\'zhao\',\'f\',to_date(\'1900/01/01\',\'YYYY/MM/DD\'));
insert into t_student(sno,name,sex,birthday) values(\'s004\',\'wang\',\'m\',to_date(\'1900/01/01\',\'YYYY/MM/DD\'));
select * from t_student;
delete from t_student;