Oracle sql例子

 create database oracle1
 create table class(id int primary key,name varchar(255))
 select * from class
 insert into class values(1,'一班')
 insert into class values(2,'二班')
 insert into class values(3,'三班')
 --创建学生表
 create table student(id int primary key,name varchar(255),cid int ,constraint FK_student_class foreign key(cid) references class(id))
 insert into student values(1,'Tom',1)
 --联合查询
 select * from student student left join class class on student.cid=class.id
 select * from class class right join student student on class.id=student.cid
 --alter
 create table school(id int,name varchar(255))
 insert into school values(1,'耶鲁大学')

 alter table school add primary key(id)
 alter table class add sid int
 alter table class add constraint FK_class_school foreign key(sid) references school(id)

 update class set sid=1 where id=1

 ---联合查询  as后面的内容是作为别名存在的，是变量不是字符串
 select school.name as 大学,class.name as 班级 ,student.name as 姓名 from student student left join class class on student.cid=class.id left join school school on class.sid=school.id
 --union all
 select name from school
 union all
 select name from class
 union all
 select name from student

 /** 查询syscolumns**/
 select * from dba_tables
 select * from dba_tables where table_name=upper('class')
 select * from user_tables where table_name=upper('class')

 --数据库本身就是有多权限的系统，有dba的tables有user的tables 个人感觉Oracle的权限分配比sql Server2005要清晰明确的多