select去重 sqlserver_SQL Server三种数据表数据去重方法
数据去重方法1:
当表中最在最大流水号时候，我们可以通过关联的方式为每条重复的记录获取唯一值
数据去重方法2:
为表中记录，按照指定字段进行群组，并获取最大流水号，然后再进行去重操作
数据去重方法3:
采用分组后，重复数据组内排名，如果排名大于1代表是重复数据行数据
三种去重方法效率对比:
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','猫猫小屋') --2
insert into test(sort,info)values('B','mssql_blog') --3
insert into test(sort,info)values('B','优秀的sql——blog') --4
insert into test(sort,info)values('B','maomao365') --5
insert into test(sort,info)values('C','sql优化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','猫猫小屋')
insert into test(sort,info)values('B','mssql_blog')
insert into test(sort,info)values('B','优秀的sql——blog')
insert into test(sort,info)values('B','maomao365')
insert into test(sort,info)values('C','sql优化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','猫猫小屋')
insert into test(sort,info)values('B','mssql_blog')
insert into test(sort,info)values('B','优秀的sql——blog')
insert into test(sort,info)values('B','maomao365')
insert into test(sort,info)values('C','sql优化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