SQL语言简单入门
此篇摘自网络。对SQL方面总结的比较全面，故转录与此，以便日后需要查阅时方便。
SQL Server 2005提供了很多的新特性，但是这些新特性是否值得冒险尝试最新的发布?根据你自身的需要来帮助评估这些新的能力吧。
现在是网络时代，大大提高了大家互相之间的数据共享，于是出现了数据库，而sql语言作为对数据库的标准查询语言大大简化了程序员的工作，使程序员更多的精力可以放在程序上，而不是数据库上。下面我举一些sql语句的例子共大家学习参考，如有不当欢迎批评指正
建表：
create table Teacher(
Tno integer primary key,
Tname char(6) not null,
Title char(6),
Dept char(10));
插入数据：
insert into Teacher values(101,'李华','讲师','计算机');
insert into Teacher values (102,'张丽','讲师','通信');
insert into Teacher values (103,'刘力伟','助教','计算机');
insert into Teacher(Tno,Tname,Dept) values (104,'李春生','计算机');
insert into Teacher(Tno,Tname,Dept) values (105,'王华英','自动化');
查询：
select * from teacher;
select * from teacher where dept='通信';
select distinct dept from teacher;
select count(*) from teacher;
select count(distinct dept) from teacher;
select * from teacher aa,teacher bb where aa.tno=bb.tno;
select Distinct Tno from course where 2<=(select count(*)from Course aa where aa.Tno=course.tno);
视图：
create view v_t_c
as
select Teacher.Tno,Tname,Title,Dept,Cno,Cname
from Teacher,course
where Teacher.Tno=course.Tno;
集合运算：
select * from teacher
union
select * from teacher_copy;
索引：
create Table Course(
Cno integer not null,
Tno integer not null,
Cname char(10) not null,
credit numeric(3,1) not null);
//insert into Course
//values(1,101,'数据库',3.5);
//insert into Course
//values(1,103,'数据库',3.5);
//insert into Course
//values(2,102,'网络',3);
//insert into Course
//values(2,101,'网络',3);
//insert into Course
//values(3,103,'操作系统',3);
//
//select * from course;
//
//delete from course;
//
//create unique index course_ind on course(Tno,Cno);
认识null：
create table Teacher(
Tno integer Primary Key,
Tname char(6) not null,
Title char(6),
Dept char(10));
insert into Teacher values (901,'李华','讲师','计算机');
insert into Teacher values (902,'张丽','讲师','通信');
insert into Teacher values (903,'刘力伟','助教','计算机');
insert into Teacher values (904,'赵莺',null,'计算机');
insert into Teacher values (905,'张大军',null,null);
select * from teacher;
Select * from teacher where title is null;
select * from teacher where dept is not null;
嵌套：
//select sname,dept from student
//where sno in(select sno
//from sc
//where cno=2);
select sname,dept from student
where sno in(select sno
from sc
where cno in(select cno
from course
where cname='网络'));
修改删除：
//update student
//set dept='通信工程'
//where dept='通信';
//select * from student;
//delete from student where dept='计算机';
//select * from student;
delete from student;
select * from student;
外键：
create table father_t
(Cno integer primary key,
Cname char(10) not null,
Credit numeric(3,1) );
create table son_t
(st_no integer primary key,
fk_cno integer,
grade integer,
foreign key(fk_cno)
references father_t(Cno));
外键数据插入：
insert into father_t
values
(1,'数据库',2);
insert into father_t
values
(2,'网络',3);
insert into son_t
values
(101,2,86);
insert into son_t
values
(102,5,78);
事务：
begin transaction
select * from teacher;
update teacher
set title=null
where tno=101;
select * from teacher;
rollback;
select * from teacher;