create table tb (name varchar(10), startdate datetime, enddate datetime)insert into tb select 'name1' , '2004-09-23' , '2004-09-30' union all select 'name1' , '2004-09-25' , '2004-09-30' union all select 'name2' , '2004-09-26' , '2005-01-03' union all select 'name1' , '2004-09-26' , '2004-09-30' delete from tb where name+convert(char(10),startdate,120)+convert(char(10),enddate,120) in (select name+convert(char(10),startdate,120)+convert(char(10),enddate,120) from tb a where exists (select 1 from tb where name=a.name and enddate=a.enddate and startdate>a.startdate) )select * from tbname startdate enddate ---- ---------- ---------- name2 2004-09-26 2005-01-03 name1 2004-09-26 2004-09-30 (所影响的行数为 2 行)
再提供一个例子(我用的是一、b)删除重复数据
一、具有主键的情况 a.具有唯一性的字段id(为唯一主键) delect table where id not in ( select max(id) from table group by col1,col2,col3... ) group by 子句后跟的字段就是你用来判断重复的条件,如只有col1, 那么只要col1字段内容相同即表示记录相同。
b.具有联合主键 假设col1+','+col2+','...col5 为联合主键 select * from table where col1+','+col2+','...col5 in ( select max(col1+','+col2+','...col5) from table where having count(*)>1 group by col1,col2,col3,col4 ) group by 子句后跟的字段就是你用来判断重复的条件, 如只有col1,那么只要col1字段内容相同即表示记录相同。
or select * from table where exists (select 1 from table x where table.col1 = x.col1 and table.col2= x.col2 group by x.col1,x.col2 having count(*) >1)
c:判断所有的字段 select * into #aa from table group by id1,id2,.... delete table insert into table select * from #aa
二、没有主键的情况
a:用临时表实现 select identity(int,1,1) as id,* into #temp from ta delect #temp where id not in ( select max(id) from # group by col1,col2,col3... ) delete table ta inset into ta(...) select ..... from #temp
b:用改变表结构(加一个唯一字段)来实现 alter table 表 add newfield int identity(1,1) delete 表 where newfield not in ( select min(newfield) from 表 group by 除newfield外的所有字段 )
alter table 表 drop column newfield
DELETE FROM tablename WHERE (id NOT IN (SELECT max(a.id) FROM nnn a ,nnn b where a.name = b.name AND a.endtime = b.endtime AND a.starttime > b.starttime group by a.name))
DELETE FROM tablename WHERE (id NOT IN (SELECT max(a.id) FROM tablename a ,tablename b where a.name = b.name AND a.endtime = b.endtime AND a.starttime > b.starttime group by a.name))
(name varchar(10),
startdate datetime,
enddate datetime)insert into tb
select 'name1' , '2004-09-23' , '2004-09-30' union all
select 'name1' , '2004-09-25' , '2004-09-30' union all
select 'name2' , '2004-09-26' , '2005-01-03' union all
select 'name1' , '2004-09-26' , '2004-09-30'
delete from tb where name+convert(char(10),startdate,120)+convert(char(10),enddate,120) in
(select name+convert(char(10),startdate,120)+convert(char(10),enddate,120) from tb a
where exists
(select 1 from tb where name=a.name
and enddate=a.enddate and startdate>a.startdate)
)select * from tbname startdate enddate
---- ---------- ----------
name2 2004-09-26 2005-01-03
name1 2004-09-26 2004-09-30
(所影响的行数为 2 行)
一、具有主键的情况
a.具有唯一性的字段id(为唯一主键)
delect table
where id not in
(
select max(id) from table group by col1,col2,col3...
)
group by 子句后跟的字段就是你用来判断重复的条件,如只有col1,
那么只要col1字段内容相同即表示记录相同。
b.具有联合主键
假设col1+','+col2+','...col5 为联合主键
select * from table where col1+','+col2+','...col5 in (
select max(col1+','+col2+','...col5) from table
where having count(*)>1
group by col1,col2,col3,col4
)
group by 子句后跟的字段就是你用来判断重复的条件,
如只有col1,那么只要col1字段内容相同即表示记录相同。
or
select * from table where exists (select 1 from table x where table.col1 = x.col1 and
table.col2= x.col2 group by x.col1,x.col2 having count(*) >1)
c:判断所有的字段
select * into #aa from table group by id1,id2,....
delete table
insert into table
select * from #aa
二、没有主键的情况
a:用临时表实现
select identity(int,1,1) as id,* into #temp from ta
delect #temp
where id not in
(
select max(id) from # group by col1,col2,col3...
)
delete table ta
inset into ta(...)
select ..... from #temp
b:用改变表结构(加一个唯一字段)来实现
alter table 表 add newfield int identity(1,1)
delete 表
where newfield not in
(
select min(newfield) from 表 group by 除newfield外的所有字段
)
alter table 表 drop column newfield