sql重复记录查询与剔除

mysql> create temporary table tmp_wrap select * from users_groups group by uid having count(1) >= 1;
Query OK,?7 rows affected (0.11 sec)
Records:?7? Duplicates: 0? Warnings: 0

mysql> truncate table users_groups;
Query OK, 14 rows affected (0.03 sec)

mysql> insert into users_groups select * from tmp_wrap;
Query OK,?7 rows affected (0.03 sec)
Records:?7? Duplicates: 0? Warnings: 0

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=== 下面的方法，执行时间特别长，可能是由 "in" 的关系，慎用

1、查找表中多余的重复记录，重复记录是根据单个字段（peopleId）来判断
select?*?from?people
where?peopleId?in?(select?? peopleId??from?? people??group??by?? peopleId??having??count(peopleId)?>?1)

2、删除表中多余的重复记录，重复记录是根据单个字段（peopleId）来判断，只留有rowid最小的记录
delete?from?people?
where?peopleId??in?(select?? peopleId??from?people??group??by?? peopleId???having??count(peopleId)?>?1)
and?rowid?not?in?(select?min(rowid)?from?? people??group?by?peopleId??having?count(peopleId )>1)

3、查找表中多余的重复记录（多个字段）?
select?*?from?vitae a
where?(a.peopleId,a.seq)?in?? (select?peopleId,seq?from?vitae?group?by?peopleId,seq??having?count(*)?>?1)

4、删除表中多余的重复记录（多个字段），只留有rowid最小的记录
delete?from?vitae a
where?(a.peopleId,a.seq)?in?? (select?peopleId,seq?from?vitae?group?by?peopleId,seq?having?count(*)?>?1)
and?rowid?not?in?(select?min(rowid)?from?vitae?group?by?peopleId,seq?having?count(*)>1)

5、查找表中多余的重复记录（多个字段），不包含rowid最小的记录
select?*?from?vitae a
where?(a.peopleId,a.seq)?in?? (select?peopleId,seq?from?vitae?group?by?peopleId,seq?having?count(*)?>?1)
and?rowid?not?in?(select?min(rowid)?from?vitae?group?by?peopleId,seq?having?count(*)>1)
(二)
比方说
在A表中存在一个字段“name”，
而且不同记录之间的“name”值有可能会相同，
现在就是需要查询出在该表中的各记录之间，“name”值存在重复的项；
Select?Name,Count(*)?From?A?Group?By?Name?Having?Count(*)?>?1
如果还查性别也相同大则如下:
Select?Name,sex,Count(*)?From?A?Group?By?Name,sex?Having?Count(*)?>?1
(三)
方法一
declare?@max?integer,@id?integer
declare?cur_rows?cursor?local?for?select?主字段,count(*)?from?表名?group?by?主字段?having?count(*)?>；?1
open?cur_rows
fetch?cur_rows?into?@id,@max
while?@@fetch_status=0
begin
select?@max?=?@max?-1
set?rowcount?@max
delete?from?表名?where?主字段?=?@id
fetch?cur_rows?into?@id,@max
end
close?cur_rows
set?rowcount?0

方法二

??? 有两个意义上的重复记录，一是完全重复的记录，也即所有字段均重复的记录，二是部分关键字段重复的记录，比如Name字段重复，而其他字段不一定重复或都重复可以忽略。

　　1、对于第一种重复，比较容易解决，使用
select?distinct?*?from?tableName

就可以得到无重复记录的结果集。

　如果该表需要删除重复的记录（重复记录保留1条），可以按以下方法删除
select?distinct?*?into?#Tmp?from?tableName
drop?table?tableName
select?*?into?tableName?from?#Tmp
drop?table?#Tmp

发生这种重复的原因是表设计不周产生的，增加唯一索引列即可解决。

2、这类重复问题通常要求保留重复记录中的第一条记录，操作方法如下

假设有重复的字段为Name,Address，要求得到这两个字段唯一的结果集
select?identity(int,1,1)?as?autoID,?*?into?#Tmp?from?tableName
select?min(autoID)?as?autoID?into?#Tmp2?from?#Tmp?group?by?Name,autoID
select?*?from?#Tmp?where?autoID?in(select?autoID?from?#tmp2)

最后一个select即得到了Name，Address不重复的结果集（但多了一个autoID字段，实际写时可以写在select子句中省去此列）

(四)查询重复
select?*?from?tablename?where?id?in?(
select?id?from?tablename?
group?by?id?
having?count(id)?>?1
)

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转载自iteye：http://h819.iteye.com/blog/531197