查询数据库表结构，默认值，是否为空等

SELECT   
    表名       = case when a.colorder=1 then d.name else '' end,  
    表说明     = case when a.colorder=1 then isnull(f.value,'') else '' end,  
    字段序号   = a.colorder,  
    字段名     = a.name,  
    标识       = case when COLUMNPROPERTY( a.id,a.name,'IsIdentity')=1 then '√'else '' end,  
    主键       = case when exists(SELECT 1 FROM sysobjects where xtype='PK' and parent_obj=a.id and name in (  
                     SELECT name FROM sysindexes WHERE indid in( SELECT indid FROM sysindexkeys WHERE id = a.id AND colid=a.colid))) then '√' else '' end,  
    类型       = b.name,  
    占用字节数 = a.length,  
    长度       = COLUMNPROPERTY(a.id,a.name,'PRECISION'),  
    小数位数   = isnull(COLUMNPROPERTY(a.id,a.name,'Scale'),0),  
    允许空     = case when a.isnullable=1 then '√'else '×' end,  
    默认值     = isnull(e.text,'无'),  
    字段说明   = isnull(g.[value],'')  
FROM syscolumns a left join systypes b   
on a.xusertype=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.major_id and f.minor_id=0  
where d.name='要查的表名'    --如果只查询指定表,加上此条件  
order by a.id,a.colorder