精妙Sql语句

 

1．  判断a表中有而b表中没有的记录

select a.* from tbl1 a

left join tbl2 b

on a.key = b.key

where b.key is null

         虽然使用in也可以实现，但是这种方法的效率更高一些

2．  新建一个与某个表相同结构的表

select * into b

from a where 1<>1

3．between的用法,between限制查询数据范围时包括了边界值,not between不包括

select * from table1 where time between time1 and time2

select a,b,c, from table1 where a not between 数值1 and 数值2

4. 说明：包括所有在 TableA 中但不在 TableB和TableC 中的行并消除所有重复行而派生出一个结果表

(select a from tableA ) except (select a from tableB) except (select a from tableC)

5. 初始化表，可以将自增长表的字增长字段置为1

TRUNCATE TABLE table1

6．多语言设置数据库或者表或者order by的排序规则

         --修改用户数据库的排序规则

ater database dbname collate SQL_Latin1_General_CP1_CI_AS

--修改字段的排序规则

alter table a alter column c2 varchar(50) collate SQL_Latin1_General_CP1_CI_AS

--按姓氏笔画排序

select * from 表名 order by 列名 Collate Chinese_PRC_Stroke_ci_as

--按拼音首字母排序

select * from 表名 order by 列名 Collate Chinese_PRC_CS_AS_KS_WS

7．列出所有的用户数据表：

SELECT TOP 100 PERCENT o.name AS 表名

FROM dbo.syscolumns c INNER JOIN

      dbo.sysobjects o ON o.id = c.id AND objectproperty(o.id, N'IsUserTable') = 1 AND

      o.name <> 'dtproperties' LEFT OUTER JOIN

      dbo.sysproperties m ON m.id = o.id AND m.smallid = c.colorder

WHERE (c.colid = 1)

ORDER BY o.name, c.colid

 

8．列出所有的用户数据表及其字段信息：

SELECT TOP 100 PERCENT c.colid AS 序号, o.name AS 表名, c.name AS 列名,

      t.name AS 类型, c.length AS 长度, c.isnullable AS 允许空,

      CAST(m.[value] AS Varchar(100)) AS 说明

FROM dbo.syscolumns c INNER JOIN

      dbo.sysobjects o ON o.id = c.id AND objectproperty(o.id, N'IsUserTable') = 1 AND

      o.name <> 'dtproperties' INNER JOIN

      dbo.systypes t ON t.xusertype = c.xusertype LEFT OUTER JOIN

      dbo.sysproperties m ON m.id = o.id AND m.smallid = c.colorder

ORDER BY o.name, c.colid

9．Left，right Join的另外一种简洁的写法

select * from a,b where a.id *= b.id  --（*= 相当于 LEFT JOIN） 

select * from a,b where a.id =* b.id  --（=* 相当于 Right JOIN） 

10．Update from 和 delete from

11．得到表中最小的未使用的ID号

         SELECT (CASE WHEN EXISTS(SELECT * FROM Handle b WHERE b.HandleID = 1)

THEN MIN(HandleID) + 1 ELSE 1 END) as HandleID

FROM Handle

WHERE NOT HandleID IN (SELECT a.HandleID - 1 FROM Handle a)

12．随机取得记录

         SELECT TOP 10 * FROM T1 ORDER BY NEWID()