怎样找出重复的数据

darren77 2003-05-09 09:45:17
我的一个表中不只是否存在重复的数据,请问怎样找出这些重复的数据?
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BenDan2002 2003-05-09
select id, count(*) as N'重复次数' from yourtable group by id having count(*)>1
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happydreamer 2003-05-09

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




回复
happydreamer 2003-05-09

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




回复
yoki 2003-05-09
找出重复数据
select * from yourtable group by field1,field2....
having count(*)>1
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dapper 2003-05-09
错了 ,SORRY
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yoki 2003-05-09
if exist
(select 1 from yourtable group by field1,field2....
having count(*)>1)
print '存在'
回复
dapper 2003-05-09
SELECT ID FROM TABLE1 WHERE ID NOT IN (SELECT DISTINCT A.ID FROM TABLE1 A )
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