sql 單表/多表查詢去除重復記錄

單表distinct

多表group by

group by 必須放在 order by 和 limit之前，不然會報錯

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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

)

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)

運行會產生問題，where(a.peopleId,a.seq)這樣的寫發是通不過的！！！

轉載于:https://www.cnblogs.com/cwqcwq/p/4670638.html

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