1.查询数据库中的所有数据库名：

 SELECT Name FROM Master..SysDatabases ORDER BY Name

2.查询某个数据库中所有的表名：
 SELECT Name FROM SysObjects Where XType='U' ORDER BY Name

3.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