mssql sqlserver 三種數據表數據去重方法分享

摘要:

下文將分享三種不一樣的數據去重方法
數據去重：需根據某一字段來界定,當此字段出現大於一行記錄時，咱們就界定爲此行數據存在重複。

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數據去重方法1:

當表中最在最大流水號時候，咱們能夠經過關聯的方式爲每條重複的記錄獲取惟一值

數據去重方法2:
爲表中記錄，按照指定字段進行羣組，並獲取最大流水號，而後再進行去重操做
 
數據去重方法3:
採用分組後，重複數據組內排名，若是排名大於1表明是重複數據行數據
 
三種去重方法效率對比:
方法3 > 方法2 > 方法1
 

create table test(keyId int identity,sort varchar(10),
info varchar(20))
go

---方法1 
truncate table test ;

insert into test(sort,info)values('A','maomao365.com')--1
insert into test(sort,info)values('A','貓貓小屋') --2
insert into test(sort,info)values('B','mssql_blog') --3
insert into test(sort,info)values('B','優秀的sql——blog') --4
insert into test(sort,info)values('B','maomao365') --5
insert into test(sort,info)values('C','sql優化blog') --6
go

delete from test where test.keyId = (select max(b.keyId) from test b where test.sort=b.sort);
select * from test 
---方法2:
truncate table test ; 
insert into test(sort,info)values('A','maomao365.com')
insert into test(sort,info)values('A','貓貓小屋')
insert into test(sort,info)values('B','mssql_blog')
insert into test(sort,info)values('B','優秀的sql——blog')
insert into test(sort,info)values('B','maomao365')
insert into test(sort,info)values('C','sql優化blog')
go
delete from test 
where keyid not in(select min(keyId) from test group by sort having count(sort)>=1);
select * from test 
---方法3:
truncate table test ; 
insert into test(sort,info)values('A','maomao365.com')
insert into test(sort,info)values('A','貓貓小屋')
insert into test(sort,info)values('B','mssql_blog')
insert into test(sort,info)values('B','優秀的sql——blog')
insert into test(sort,info)values('B','maomao365')
insert into test(sort,info)values('C','sql優化blog')
go
delete A2 from (
select row_Number() over(partition by sort order by keyid) as keyId_e,* from test 
) as A2 where A2.keyId_e >1

select * from test 
go
drop table test 

 

<img src="http://www.maomao365.com/wp-content/uploads/2018/07/mssql_sqlserver_數據表數據去重的三種方法分享.png" alt="mssql_sqlserver_數據表數據去重的三種方法分享" width="813" height="749" class="size-full wp-image-6767" />

 

轉自:http://www.maomao365.com/?p=6766