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SQL删除重复数据只保留一条

2013-11-27 00:25 591 查看

--创建表

create table student(sid varchar2(4) primary key,

sname varchar2(10) not null,

sex char(6) check(sex in('男','女')))

--创建序列

create sequence seq_s

start with 1

minvalue 1

increment by 1

maxvalue 999;

--插入数据

insert into student values(seq_s.nextVal,'石1','男');

insert into student values(seq_s.nextVal,'石1','男');

insert into student values(seq_s.nextVal,'石1','男');

insert into student values(seq_s.nextVal,'石1','男');

insert into student values(seq_s.nextVal,'石1','男');

insert into student values(seq_s.nextVal,'石2','女');

insert into student values(seq_s.nextVal,'石2','女');

insert into student values(seq_s.nextVal,'石2','女');

insert into student values(seq_s.nextVal,'石2','女');

insert into student values(seq_s.nextVal,'石3','女');

insert into student values(seq_s.nextVal,'石4','女');

--查看姓名(重复的只显示一条记录)

select distinct sname from student;

--以sname分组,得到姓名和sid数量

select sname,count(sid) from student group by sname;

select sname,count(sname) from student group by sname;

select sname,count(sid),count(sname),min(sid) from student group by sname;

--以sname分组,得到重复的姓名和sid数量

select sname from student group by sname having count(sname)>1;

select sname from student group by sname having count(sid)>1;

--得到重复的所有的记录

select * from student where sname in (select sname from student group by sname having count(sid)>1);

--选出重复的最小的sid

select min(sid) from student group by sname having count(sid)>1;

--删除重复的记录，留下最小的sid

delete from student where sname in (select sname from student group by sname having count(sid)>1)

and sid not in (select min(sid) from student group by sname having count(sid)>1);

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标签： sql 重复删除

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