--删除表中的重复记录。

create table user_info

(

???? ??username varchar2(20),

?????? password varchar2(20)

)

?

insert into user_info values('JACK','123',SQ_USER.NEXTVAL);

insert into user_info values('JACK','123',SQ_USER.NEXTV);

insert into user_info values('SHININ','123',SQ_USER.NEXTVAL);

insert into user_info values('SHININ','123',SQ_USER.NEXTVAL);

insert into user_info values('SHININ','456',SQ_USER.NEXTVAL);

?

--方案一

CREATE TABLE? USER_INFO2

AS

SELECT DISTINCT * FROM USER_INFO ;

?

DROP TABLE USER_INFO;

?

RENAME USER_INFO2 TO USER_INFO;

?

SELECT * FROM USER_INFO;

?

--方案二

ALTER TABLE USER_INFO ADD ID NUMBER;

CREATE SEQUENCE SQ_USER;

DELETE FROM USER_INFO;

?

DELETE FROM USER_INFO

?????? WHERE ID NOT IN(

???????????? SELECT MIN(ID)AS ID FROM USER_INFO

???????????? GROUP BY (USERNAME,PASSWORD));