SQL基础

一、基础

1.创建数据库

create database dbname

2.删除数据库

drop database dbname

3.备份sql server

--创建备份数据的device

use master

exec sp_addumpdevice 'disk' ,'testBack','c:\mssql7\backup\MyNwind_1.dat'

--开始备份

backup database pubs to testback

4.创建新表

create table tabname(col 1 type1[not null] [primary key],co2 type2[not null]...)

根据已有的表创建新表

A:create table tab_new like tab_old(使用旧表创建新表)

B:create table tab_new as select col1,col2... from tab_old definition only

5.删除新表

drop table tabname

6.增加一列

Alter table tabname add column col type

注：列增加后将不能删除。DB2中列加上数据后数据类型也不能变，唯一能改变的是增加varchar的长度

7.添加主键：Alter table tabname add primary key(col)

删除主键：Alter table tabname drop primary key (col)

8.创建索引：create [unique] index inxname on tabname(col....)

删除索引：drop index idxname

注：索引是不可更改的，想要更改必须删除重新建

9。创建视图：create view viewname as select statement

删除视图：drop view viewname

10.几个简单基本sql语句

选择：select * from table1 where 范围

插入：insert into table1(field1,field2) values(value1,value2)

删除：delete from table1 where 范围

更新：update table 1 set field1 = value1 where 范围

查找：select * from table1 where field1 like '%value1%' --like 的语法

排序：select * from table1 order by field1,field2 desc

总数：select count as totalcount from table1

求和：select sum(field1) as sumvalue from talble1

平均：select avg(field1) as avgvalue from table1

最大：select max(field11) as maxvalue from table1

最小：select min(field1) as minvalue from table1

11.几个高级查询运算

A:UNION运算符

UNION运算符通过组合其他两个结果表