MySQL

1)显示所有数据库

show database；

2)显示所有表

show tables；

3)显示表结构

desc 表名

SQL Server

当前数据库名:

查询所有表：

select * from sysobjects where xtype='U'

某个数据库中所有的表名:

查询表结构信息:

SELECT (case when a.colorder=1 then d.name else null end) 表名,

a.colorder 字段序号,a.name 字段名,

(case when COLUMNPROPERTY( a.id,a.name,'IsIdentity')=1 then '√'else '' end) 标识,

(case when (SELECT count(*) FROM sysobjects

WHERE (name in (SELECT name FROM sysindexes

WHERE (id = a.id) AND (indid in

(SELECT indid FROM sysindexkeys

WHERE (id = a.id) AND (colid in

(SELECT colid FROM syscolumns WHERE (id = a.id) AND (name = a.name)))))))

AND (xtype = 'PK'))>0 then '√' else '' end) 主键,b.name 类型,a.length 占用字节数,

COLUMNPROPERTY(a.id,a.name,'PRECISION') as 长度,

isnull(COLUMNPROPERTY(a.id,a.name,'Scale'),0) as 小数位数,(case when a.isnullable=1 then '√'else '' end) 允许空,

isnull(e.text,'') 默认值,isnull(g.[value], ' ') AS [说明]

FROM syscolumns a

left join systypes b on a.xtype=b.xusertype

inner join sysobjects d on a.id=d.id and d.xtype='U' and d.name<>'dtproperties'

left join syscomments e on a.cdefault=e.id

left join sys.extended_properties g on a.id=g.major_id AND a.colid=g.minor_id

left join sys.extended_properties f on d.id=f.class and f.minor_id=0

where b.name is not null

--WHERE d.name='要查询的表' --如果只查询指定表,加上此条件

order by a.id,a.colorder

oracle

(1) 启动 监听

lsnrctl start；

(2)进入sqlplus界面

sqlplus  /nolog

SQL>conn sys/jiaxiaoai@orcl as sysdba;

(3)启动数据库实例

SQL>startup;

(4)查看当前所有的数据库

select name from v$database;

(5)查看哪些用户拥有sysdba、sysoper权限

select * from V_$PWFILE_USERS；

show user；查看当前数据库连接用户

(6)进入某个数据库：database 数据库名；

查看数据库结构：desc v$database；

(7)查看所有用户实例：

select instance_name from v$instance;

(8)查看当前库的所有数据表

select table_name from all_tables;

select table_name from user_tables;

select table_name from all_tables where owner='用户名';

(9)查看表结构

desc 表名；

(10)增加数据库用户

create user 用户名 identified by 密码 default tablespace users Temporary TABLESPACE Temp；

(11)用户授权

grant connect，resource，dba to 用户名；

grant sysdba to 用户名；

(12)更改数据库用户密码

alter user 用户名 identified by 密码；