SQL查出一張表中重複的所有記錄數據

1、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重複的所有數據，現在列下：

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

2、查詢出所有數據進行分組之後，和重複資料的重複次數的查詢數據，先列下：

SELECT count(username) as '重复次数',username from xi group by username  having count(*)>1 order by username desc

3、一下為查看別人的結果，現列下：查詢及刪除重複記錄的方法大全

1、查找表中多餘的重複記錄，重複記錄是根據單一欄位（peopleId）來判斷

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

2、刪除表中多餘的重複記錄，重複記錄是根據單一欄位（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，因此可以像下面的語句一樣，將查詢結果命名為一張臨時表來作為修改表資料的條件，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
    )
)

3、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)

4、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)

5、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”，
而且不同記錄之間的“name”值有可能會相同，
現在就是需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

如果還查性別也相同大則如下:

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 主欄位,count(*) from 表名group by 主欄位 having count(*) >; 1open cur_rowsfetch cur_rows into @id,@maxwhile @maxwhole = @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，一是完全重複的記錄，也即所有欄位均重複的記錄，二是部分關鍵欄位重複的記錄，例如Name欄位重複，而其他欄位不一定重複或都重複可以忽略。

　　1、對於第一種重複，比較容易解決，使用select distinct * from tableName　　就可以獲得無重複記錄的結果集。如果該表需要刪除重複的記錄（重複記錄保留1個），可以按以下方法刪除select distinct * into #Tmp from tableNamedrop table tableNameselect * into tableName from #Tmpdrop table #Tmp　　發生這種重複的原因是表設計不重複的原因是表設計不重複週產生的，增加唯一索引列即可解決。

　　2、這類重複問題通常要求保留重複記錄中的第一條記錄，操作方法如下假設有重複的字段為Name,Address，要求得到這兩個字段唯一的結果集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)　　最後一個就得到了最後一個selectName， Address不重複的結果集（但多了一個autoID字段，實際寫時可以寫在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)