sql 查出一張表中重複的全部記錄數據

一、在面試的時候碰到一個 問題，就是讓寫一張表中有id和name 兩個字段，查詢出name重複的全部數據，如今列下：

select * from xi a where (a.username) in  (select username from xi group by username  having count(*) > 1)

二、查詢出全部數據進行分組以後，和重複數據的重複次數的查詢數據，先列下：

select  count(username) as '重複次數',username from xi group by username  having count(*)>1 order by username desc

三、一下爲 查看別人的 結果，現列下：查詢及刪除重複記錄的方法大全

一、查找表中多餘的重複記錄，重複記錄是根據單個字段（peopleId）來判斷

select * from people
where peopleId in (select  peopleId  from  people  group  by  peopleId  having  count(peopleId) > 1)

二、刪除表中多餘的重複記錄，重複記錄是根據單個字段（peopleId）來判斷，只留有rowid最小的記錄

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)

另外，MySQL中使用上面的SQL會報錯：You can't specify target table 'XXX' for update in FROM clause,不能在修改表的同時去查詢同一張表，所以能夠像下面的語句同樣，將查詢結果命名爲一張臨時表來做爲修改表數據的條件，以規避上述錯誤。

delete from user where user_id in(
    (select user_id from 
        (select c.* from cab_user c where c.extra_id in 
            (select  a.extra_id  from user a group  by  a.extra_id having  count(a.extra_id) > 1) and c.user_id not in 
            (select min(b.user_id) from  user b group by b.extra_id having count(b.extra_id )>1)
        ) d
    )
)

三、查找表中多餘的重複記錄（多個字段）

select * from vitae a
where (a.peopleId,a.seq) in  (select peopleId,seq from vitae group by peopleId,seq  having count(*) > 1)

四、刪除表中多餘的重複記錄（多個字段），只留有rowid最小的記錄

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)

五、查找表中多餘的重複記錄（多個字段），不包含rowid最小的記錄

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)
比方說
在A表中存在一個字段「name」，
並且不一樣記錄之間的「name」值有可能會相同，
如今就是須要查詢出在該表中的各記錄之間，「name」值存在重複的項；

Select Name,Count(*) From A Group By Name Having Count(*) > 1

若是還查性別也相同大則以下:

Select Name,sex,Count(*) From A Group By Name,sex Having Count(*) > 1

(三)
方法一declare @max integer,@id integerdeclare cur_rows cursor local for select 主字段,count(*) from 表名 group by 主字段 having count(*) >； 1open cur_rowsfetch cur_rows into @id,@maxwhile @@fetch_status=0beginselect @max = @max -1set rowcount @maxdelete from 表名 where 主字段 = @idfetch cur_rows into @id,@maxendclose cur_rowsset rowcount 0

方法二＂重複記錄＂有兩個意義上的重複記錄，一是徹底重複的記錄，也即全部字段均重複的記錄，二是部分關鍵字段重複的記錄，好比Name字段重複，而其餘字段不必定重複或都重複能夠忽略。

　　一、對於第一種重複，比較容易解決，使用select distinct * from tableName　　就能夠獲得無重複記錄的結果集。　　若是該表須要刪除重複的記錄（重複記錄保留1條），能夠按如下方法刪除select distinct * into #Tmp from tableNamedrop table tableNameselect * into tableName from #Tmpdrop table #Tmp　　發生這種重複的緣由是表設計不周產生的，增長惟一索引列便可解決。

　　二、這類重複問題一般要求保留重複記錄中的第一條記錄，操做方法以下　　假設有重複的字段爲Name,Address，要求獲得這兩個字段惟一的結果集select identity(int,1,1) as autoID, * into #Tmp from tableNameselect min(autoID) as autoID into #Tmp2 from #Tmp group by Name,autoIDselect * from #Tmp where autoID in(select autoID from #tmp2)　　最後一個select即獲得了Name，Address不重複的結果集（但多了一個autoID字段，實際寫時能夠寫在select子句中省去此列）

(四)
查詢重複

select * from tablename where id in (select id from tablenamegroup by idhaving count(id) > 1)

文章轉自：http://blog.csdn.net/a1108501...