查表的字段名，主键，字段类型

一、oracle

1、获取当前oracle数据库中的所有表

select table_name from user_tables

2、查询某个表中的字段名称、类型、精度、长度、是否为空  

select COLUMN_NAME,DATA_TYPE,DATA_PRECISION,DATA_SCALE,NULLABLE    
from user_tab_columns    
where table_name ='YourTableName'  
3、查询某个表中的主键字段名  

select col.column_name    
from user_constraints con,  user_cons_columns col    
where con.constraint_name = col.constraint_name    
and con.constraint_type='P'    
and col.table_name = 'YourTableName'  
4、查询某个表中的外键字段名称、所引用表名、所应用字段名  

select distinct(col.column_name),r.table_name,r.column_name    
from    
user_constraints con,   
user_cons_columns col,    
(select t2.table_name,t2.column_name,t1.r_constraint_name    
from user_constraints t1,user_cons_columns t2    
where t1.r_constraint_name=t2.constraint_name    
and t1.table_name='YourTableName'  
) r    
where con.constraint_name=col.constraint_name    
and con.r_constraint_name=r.r_constraint_name    
and con.table_name='YourTableName' 
5、如何从Oracle中取得表的注释

       user_tab_comments;表注释

        user_col_comments;表字段注释

　 以上两个只能获取自己用户的表的注释信息，如果要访问自己

能够访问的其他用户的表，则需要使用：

        all_tab_comments;表注释

        all_col_comments;表字段注释

　 当然，如果有DBA权限，则可以使用

        dba_tab_comments;表注释

        dba_col_comments;表字段注释

　 dba*和all*最好指定owner条件。user*没有该字段

        user_tab_comments;表注释

        user_col_comments;表字段注释

 

二、SQLServer

1、读取库中的所有表名

　　select name from sysobjects where xtype='u' 

2、字段 

SELECT c.name,t.name,c.xprec,c.xscale,c.isnullable    
FROM systypes t,syscolumns c    
WHERE t.xtype=c.xtype    
AND c.id = (SELECT id FROM sysobjects WHERE name='YourTableName')    
ORDER BY c.colid   
3、主键（参考SqlServer系统存储过程sp_pkeys）  

select COLUMN_NAME = convert(sysname,c.name)                  
from                                                          
sysindexes i, syscolumns c, sysobjects o                      
where o.id = object_id('[YourTableName]')                     
and o.id = c.id                                               
and o.id = i.id                                               
and (i.status & 0x800) = 0x800                                
and (c.name = index_col ('[YourTableName]', i.indid,  1) or        
     c.name = index_col ('[YourTableName]', i.indid,  2) or        
     c.name = index_col ('[YourTableName]', i.indid,  3) or        
     c.name = index_col ('[YourTableName]', i.indid,  4) or        
     c.name = index_col ('[YourTableName]', i.indid,  5) or        
     c.name = index_col ('[YourTableName]', i.indid,  6) or        
     c.name = index_col ('[YourTableName]', i.indid,  7) or        
     c.name = index_col ('[YourTableName]', i.indid,  or        
     c.name = index_col ('[YourTableName]', i.indid,  9) or        
     c.name = index_col ('[YourTableName]', i.indid, 10) or        
     c.name = index_col ('[YourTableName]', i.indid, 11) or        
     c.name = index_col ('[YourTableName]', i.indid, 12) or        
     c.name = index_col ('[YourTableName]', i.indid, 13) or        
     c.name = index_col ('[YourTableName]', i.indid, 14) or        
     c.name = index_col ('[YourTableName]', i.indid, 15) or        
     c.name = index_col ('[YourTableName]', i.indid, 16)          
     )   
4、外键  

select t1.name,t2.rtableName,t2.name    
from    
(select col.name, f.constid as temp    
from syscolumns col,sysforeignkeys f    
where f.fkeyid=col.id    
and f.fkey=col.colid    
and f.constid in    
( select distinct(id)     
   from sysobjects    
   where OBJECT_NAME(parent_obj)='YourTableName'    
   and xtype='F'    
  )    
) as t1 ,    
(select OBJECT_NAME(f.rkeyid) as rtableName,col.name, f.constid as temp    
from syscolumns col,sysforeignkeys f    
where f.rkeyid=col.id    
and f.rkey=col.colid    
and f.constid in    
( select distinct(id)    
   from sysobjects    
   where OBJECT_NAME(parent_obj)='YourTableName'    
   and xtype='F'    
)    
) as t2    
where t1.temp=t2.temp
三、Access

1、所有表清单

conn.Open();
    dt= conn.GetOleDbSchemaTable(OleDbSchemaGuid.Tables, new object[] { null, null, null, "TABLE" });
2、表结构

conn.Open();

   dtColumnsInfo = conn.GetOleDbSchemaTable(OleDbSchemaGuid.Columns, new object[] { null, null, strTableName,null });