視頻課：https://edu.csdn.net/course/play/7940

Create table test

(id number(2),

?names varchar2(20));

?insert into test values(1,'張三');
?insert into test values(2,'李四');
?insert into test values(3,'馬七');

?select * from test;

?--查找重復(fù)數(shù)據(jù)
select * from test a where (a.id,a.names) in

?(select id,names from test group by id,names having count(*) > 1)

?--刪除重復(fù)數(shù)據(jù)，只留rowid最小的那行；
?delete from test a where (a.id,a.names) in

?(select id,names from test group by id,names having count(*) > 1)

? and rowid not in (select min(rowid) from test group by id,names having count(*)>1)
? --查找重復(fù)數(shù)據(jù)，不含rowid最小的行
? select * from test a where (a.id,a.names) in
? (select id,names from test group by id,names having count(*) > 1)
? and rowid not in (select min(rowid) from test group by id,names having count(*)>1)
?

---1.以上是重復(fù)數(shù)據(jù)根據(jù)多列來判斷

以下是重復(fù)數(shù)據(jù)根據(jù)單列來判斷

1、首先，查找表中多余的重復(fù)記錄，重復(fù)記錄是根據(jù)單個字段（id）來判斷

?

select * from test where id in(select id from test group by having count(id) >1)

?

2、刪除表中多余的重復(fù)記錄，重復(fù)記錄是根據(jù)單個字段（id）來判斷，只留有rowid最小的記錄

?

delete from test where (id) in (select id from test group by id having count(id) >1) and rowid not in (select min(rowid) from test group by id having count(*)>1)

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