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sql如何去重查詢

coldplay.xixi

發布： 2020-10-10 11:37:29

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sql去重查詢的方法：重複記錄根據單個字段peopleId來判斷，使用語句刪除，代碼為【where peopleId in (select peopleId from people group by peopleId 】。

sql如何去重查詢

sql去重查詢的方法：

sql 單表/多表查詢移除重複記錄

單表distinct

多表group by

group by 必須放在order by 和limit之前，不然會報錯

1、查找表中多餘的重複記錄，重複記錄是根據單一字段（peopleId）來判斷

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

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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)

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3、查找表中多餘的重複記錄（多個欄位）

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

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4、刪除表中多餘的重複記錄（多個欄位），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)

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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)

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(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

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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

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(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

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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，也即所有字段均重複的記錄，二是部分關鍵字段重複的記錄，比如Name字段重複，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

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就可以得到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筆），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

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發生這種重複的原因是表設計不周產生的，增加唯一索引列即可解決。

2、這類重複問題通常要求保留重複記錄中的第一筆記錄，操作方法如下

假設有重複的欄位為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)

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最後一個select即得到了Name，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 tablename
group by id
having count(id) > 1
)

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3、尋找表中多餘的重複記錄（多個欄位）

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

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

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