select *,
field1=(case when ordering=(select ordering from tb a where not exists(select 1 from tb
where a.category=category and a.ordering<ordering)) then 'first' else null end),
field2=(case when ordering=(select ordering from tb a where not exists(select 1 from tb
where a.category=category and a.ordering>ordering)) then 'first' else null end),
from tb
field1=(case when ordering=(select ordering from tb a where not exists(select 1 from tb
where a.category=category and a.ordering<ordering)) then 'first' else null end),
field2=(case when ordering=(select ordering from tb a where not exists(select 1 from tb
where a.category=category and a.ordering>ordering)) then 'last' else null end),
from tb
CASE WHEN
NOT EXISTS(SELECT 1 FROM TB WHERE category=T.category AND ordering<T.ordering)
THEN 'first' ELSE NULL END AS field1,
CASE WHEN
NOT EXISTS(SELECT 1 FROM TB WHERE category=T.category AND ordering>T.ordering)
THEN 'last' ELSE NULL END AS field2FROM TB T
----------------------------------------------------------------
-- Author :fredrickhu(小F 向高手学习)
-- Date :2009-06-17 20:59:03
----------------------------------------------------------------
--> 测试数据:[tb]
if object_id('[tb]') is not null drop table [t1]
create table [tb]([id] int,[productname] varchar(6),[category] varchar(1),[ordering] int)
insert [tb]
select 1,'apple','A',0 union all
select 2,'orange','A',1 union all
select 3,'bike','B',0 union all
select 4,'car','B',1 union all
select 5,'ship','B',2
--------------开始查询--------------------------
SELECT * ,
CASE WHEN
NOT EXISTS(SELECT 1 FROM TB WHERE category=T.category AND ordering<T.ordering)
THEN 'first' ELSE NULL END AS field1,
CASE WHEN
NOT EXISTS(SELECT 1 FROM TB WHERE category=T.category AND ordering>T.ordering)
THEN 'last' ELSE NULL END AS field2FROM TB T
----------------结果----------------------------
/* [id] [productname] [category] [ordering] field1 field2
1 apple A 0 first NULL
2 orange A 1 NULL last
3 bike B 0 first NULL
4 car B 1 NULL NULL
5 ship B 2 NULL last*/
子查询返回的值多于一个。当子查询跟随在 =、!=、<、<=、>、>= 之后,或子查询用作表达式时,这种情况是不允许的。
看看这个你就知道了 --处理表重复记录(查询和删除)
/******************************************************************************************************************************************************
1、Num、Name相同的重复值记录,没有大小关系只保留一条
2、Name相同,ID有大小关系时,保留大或小其中一个记录
整理人:中国风(Roy)日期:2008.06.06
******************************************************************************************************************************************************/--1、用于查询重复处理记录(如果列没有大小关系时2000用生成自增列和临时表处理,SQL2005用row_number函数处理)--> --> (Roy)生成測試數據
if not object_id('Tempdb..#T') is null
drop table #T
Go
Create table #T([ID] int,[Name] nvarchar(1),[Memo] nvarchar(2))
Insert #T
select 1,N'A',N'A1' union all
select 2,N'A',N'A2' union all
select 3,N'A',N'A3' union all
select 4,N'B',N'B1' union all
select 5,N'B',N'B2'
Go
--I、Name相同ID最小的记录(推荐用1,2,3),方法3在SQl05时,效率高于1、2
方法1:
Select * from #T a where not exists(select 1 from #T where Name=a.Name and ID<a.ID)方法2:
select a.* from #T a join (select min(ID)ID,Name from #T group by Name) b on a.Name=b.Name and a.ID=b.ID方法3:
select * from #T a where ID=(select min(ID) from #T where Name=a.Name)方法4:
select a.* from #T a join #T b on a.Name=b.Name and a.ID>=b.ID group by a.ID,a.Name,a.Memo having count(1)=1 方法5:
select * from #T a group by ID,Name,Memo having ID=(select min(ID)from #T where Name=a.Name)方法6:
select * from #T a where (select count(1) from #T where Name=a.Name and ID<a.ID)=0方法7:
select * from #T a where ID=(select top 1 ID from #T where Name=a.name order by ID)方法8:
select * from #T a where ID!>all(select ID from #T where Name=a.Name)方法9(注:ID为唯一时可用):
select * from #T a where ID in(select min(ID) from #T group by Name)--SQL2005:方法10:
select ID,Name,Memo from (select *,min(ID)over(partition by Name) as MinID from #T a)T where ID=MinID方法11:select ID,Name,Memo from (select *,row_number()over(partition by Name order by ID) as MinID from #T a)T where MinID=1生成结果:
/*
ID Name Memo
----------- ---- ----
1 A A1
4 B B1
field1=(case when ordering =(select ordering from (select ordering ,category from tb a where not exists(select 1 from tb
where a.category=category and a.ordering>ordering)) a where a.category=c.category ) then 'first' else null end),
field2=(case when ordering =(select ordering from (select ordering ,category from tb a where not exists(select 1 from tb
where a.category=category and a.ordering<ordering)) a where a.category=c.category ) then 'last' else null end)
from tb c-----------------------------------
1 apple A 0 first NULL
2 orange A 1 NULL last
3 bike B 0 first NULL
4 car B 1 NULL NULL
5 ship B 2 NULL last
case when ordering = (select min(ordering) from T as a where a.pid = t.pid) then 'first' else null end as field1,
case when ordering = (select max(ordering) from T as b where b.pid = t.pid) then 'last' else null end as field2
from T