SQLServer数据集合的交、并、差集运算
SQLServer2005通过intersect,union,except和三个关键字对应交、并、差三种集合运算。
他们的对应关系可以参考下面图示
相关测试实例如下：
use tempdb
go
if (object_id ('t1' ) is not null ) drop table t1
if (object_id ('t2' ) is not null ) drop table t2
go
create table t1 (a int )
insert into t1 select 1 union select 2 union select 3
create table t2 (a int )
insert into t2 select 3 union select 4 union select 5
go
select * from t1 union select * from t2
go
/* 求表并集
1
2
3
4
5*/
select * from t1 union all select * from t2
go
/*求表并集不过滤重复
1
2
3
3
4
5*/
select * from t1 except select * from t2
go
/*求t1对t2的差集
1
2*/
select * from t1 intersect select * from t2
go
/*求t1对t2的交集
3*/
本文来自CSDN博客，转载请标明出处：http://blog.csdn.net/jinjazz/archive/2009/09/07/4527863.aspx
相关文档：
sqlserver2005有关键字ntile(x)和over(partition by.. order by..)子句配合.
比如获取每个表的前10%个字段。
select id , name , colid , rn from (
select * , rn = ntile (10 )
over (partition by id order by colorder )
from syscolumns )t where rn = 1 ......
if (object_id ('t' ) is not null ) drop table t
go
create table t (id int identity (1 , 1 ), name varchar (40 ))
go
insert into t (name ) select newid ()
go 10
select * from t
/*
1 18C1C418-9029-4599-8D5E-616354A113C8
2 A0FE1177-09D8-4C56-9FB5-C2FA ......
Declare @Id int
Declare @Name varchar(20)
Declare Cur Cursor For Select Id,Name from T_User
Open Cur
Fetch next from Cur Into @Id,@Name
While @@fetch_status=0
Begin
Update T_User Set [Name]=@Name,Id=@Id
......
原文转自:http://dev.csdn.net/develop/article/71/71778.shtm
大多数SQL Server表需要索引来提高数据的访问速度，如果没有索引，SQL Server要进行表格扫描读取表中的每一个记录才能找到索要的数据。索引可以分为簇索引和非簇索引，簇索引通过重排表中的数据来提高数据的访问速度，而非簇索引则通过维护表中的数 ......
