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

原文地址:https://www.cnblogs.com/lhws/p/1747629.html