sql如何去重查詢

sql去重查詢的方法:重復記錄根據單個字段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

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!??!

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