T-SQL实用查询之常用SQL语句

删除数据库所有的表：

declare @sql varchar()
while (select count(*) from sysobjects where type='U')>
begin
SELECT @sql='drop table ' + name
FROM sysobjects
WHERE (type = 'U')
ORDER BY 'drop table ' + name
exec(@sql)
end

查询表的字段信息：

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
 and d.name='tablename'
 order by a.id,a.colorder

http://jingyan.baidu.com/article/9c69d48f99a91b13c9024ebf.html

判断字段是否包含中文字符：

 ---一个中文字符占2个字节
 select len(Type),datalength(Type),type from T_Visas where len(Type)=datalength(Type)

查询表中的某个列是否有重复值出现的sql语句

select 某列,COUNT() from table group by 某列 order by count()