>>mysql :
1、查看所有表名：
show tables [from db_name];
2、查看字段信息
SHOW FULL COLUMNS FROM db_name.table_name
獲取以下信息
Field：字段名
Type：字段類型
Collation：字符集（mysql 5.0以上有）
Null：是否可以爲NULL
Key：索引（PRI,unique,index)
Default：缺省值
Extra：額外（是否 auto_increment)
Privileges：權限
Comment：備註（mysql 5.0以上有)
>>sqlserver
1、查看所有用戶建表名
select name from Sysobjects where xtype='U' order by name;
2、查看字段信息
SELECT
a.colorder as字段順序號,
a.name as字段名稱,
a.collation as排序字符集,
是否自動增長數字=case when COLUMNPROPERTY( a.id,a.name,'IsIdentity')=1 then 'yes'else 'no' end,
是否主鍵=case when exists(SELECT 1 FROM sysobjects where xtype='PK' and name in (
SELECT name FROM sysindexes WHERE indid in(
SELECT indid FROM sysindexkeys WHERE id = a.id AND colid=a.colid
))) then 'yes' else 'no' end,
字段類型=b.name,
字段長度=a.length,
字段字符長度=COLUMNPROPERTY(a.id,a.name,'PRECISION'),
小數位數=isnull(COLUMNPROPERTY(a.id,a.name,'Scale'),0),
是否爲NULL=case when a.isnullable=1 then 'yes'else 'no' end,
缺省值=isnull(e.text,'')
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' or d.xtype='V') and d.name<>'dtproperties'
left join syscomments e on a.cdefault=e.id
where d.name='purchase_medicine'
order by a.colorder
>>oracle
//查詢所有表的信息
select * from dba_tables
//查詢所有視圖的信息
select * from dba_views
//查詢指定表或視圖的列信息
select * from dba_tab_columns
注意：當要創建包含Sys表空間的對象時，需要賦相應表或視圖的權限給它。
如需要創建查詢包含表和視圖的視圖
create or replace view v_tableview
as
select owner , table_name from dba_tables
union all
select owner , view_name from dba_views
則需要
grant select on sys.dba_tables to "用戶"
grant select on sys.dba_views to "用戶"