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 group by col1,col2,col3,col4 having count(*)>1 ) 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 #tempb: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
我已试过了,一条记录没多也一条没少,我还曾试着用inner join 来联接first和second来进行匹配选择,但记录数突然成了原记录数的3倍多,搞得我头大了五六个! How should I do next?
1. select tb1.name,b.address,b.phone into last from (select distinct name from first) as tb1,first b where tb1.name = b.name 2. 同上
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
group by col1,col2,col3,col4
having count(*)>1
)
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 #tempb: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
How should I do next?
select tb1.name,b.address,b.phone into last
from (select distinct name from first) as tb1,first b
where tb1.name = b.name
2. 同上