mysql 數據表中查找、刪除重復記錄 - langtianya－IT工程師數位筆記本

文章出處

為了性能考慮，在閱讀之前提醒大家，如果有子查詢，子查詢查詢到的數據最好不要超過總數據量的30%。

查詢有重復數據的記錄

select * from F group by a,b,c,d having count(*)>1

select distinct * into #Tmp from tableName
drop table tableName
select * into tableName from #Tmp
drop table #Tmp

SQL刪除重復數據方法

例如：

id           name         value 
1               a                 pp 
2               a                 pp 
3               b                 iii 
4               b                 pp 
5               b                 pp 
6               c                 pp 
7               c                 pp 
8               c                 iii

id是主鍵 
要求得到這樣的結果

id           name         value 
1               a                 pp 
3               b                 iii 
4               b                 pp 
6               c                 pp 
8               c                 iii

方法1

delete YourTable where [id] not in ( select max([id]) from YourTable group by (name + value))

方法2

delete a from 表 a left join( select id=min(id) from 表 group by name,value )b on a.id=b.id where b.id is null

查詢及刪除重復記錄的SQL語句查詢及刪除重復記錄的SQL語句

1、查找表中多余的重復記錄，重復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)

2、刪除表中多余的重復記錄，重復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)

3、查找表中多余的重復記錄（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、刪除表中多余的重復記錄（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、查找表中多余的重復記錄（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”值存在重復的項；

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 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

＂重復記錄＂有兩個意義上的重復記錄，一是完全重復的記錄，也即所有字段均重復的記錄，二是部分關鍵字段重復的記錄，比如Name字段重復，而其他字段不一定重復或都重復可以忽略。　　

1、對于第一種重復，比較容易解決，使用 select distinct * from tableName 　　就可以得到無重復記錄的結果集。　　如果該表需要刪除重復的記錄（重復記錄保留1條），可以按以下方法刪除

select distinct * into #Tmp from tableName drop table tableName select * into tableName from #Tmp drop table #Tmp 　　

發生這種重復的原因是表設計不周產生的，增加唯一索引列即可解決。　　

2、這類重復問題通常要求保留重復記錄中的第一條記錄，操作方法如下　　假設有重復的字段為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 tableName select min(autoID) as autoID into #Tmp2 from #Tmp group by Name,autoID select * from #Tmp where autoID in(select autoID from #tmp2) 　

　最后一個select即得到了Name，Address不重復的結果集（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) 查詢重復

select * from tablename where id in ( select id from tablename group by id having count(id) > 1 )

去重：

-- //////////////////////////////////實現1
    DELETE 
FROM
    tableName t1
WHERE
    t1.id NOT IN (
        SELECT
            *
        FROM
            (
                SELECT
                    min(t3.id)
                FROM
                    tableName t3
                GROUP BY
                    column1（即去重的字段）
            ) t2
    ) 

-- //////////////////////////////////實現2
    DELETE 
FROM
    tableName t1
WHERE
    t1.id NOT IN (
        SELECT
            *
        FROM
            (
                SELECT DISTINCT
                    id 
                FROM
                    tableName t3
            ) t2
    )