1.删除重复记录(当表中无主键时)
create table TESTTB(
bm varchar(4),
mc varchar2(20)
)
insert into TESTTB values(1,'aaaa');
insert into TESTTB values(1,'aaaa');
insert into TESTTB values(2,'bbbb');
insert into TESTTB values(2,'bbbb');
/*方案一*/
delete from TESTTB where rowid not in
(select max(rowid) from TESTTB group by TESTTB.BM,TESTTB.MC)
/*方案二*/
delete from TESTTB a where a.rowid!= (
select max(rowid) from TESTTB b where a.bm=b.bm and a.mc=b.mc
)
2.bookEnrol是用来登记的，不管你是借还是还，都要添加一条记录。
请写一个SQL语句，获取到现在状态为已借出的所有图书的相关信息，
ID为3的java书，由于以归还，所以不要查出来。要求查询结果应为：(被借出的书和被借出的日期)
create table book(
id int ,
name varchar2(30),
PRIMARY KEY (id)
)
insert into book values(1,'English');
insert into book values(2,'Math');
insert into book values(3,'JAVA');
create table bookEnrol(
id int,
bookId int,
dependDate date,
state int,
FOREIGN KEY (bookId) REFERENCES book(id) ON DELETE CASCADE
)
insert into bookEnrol values(1,1,to_date('2009-01-02','yyyy-mm-dd'),1);
insert into bookEnrol values(2,1,to_date('2009-01-12','yyyy-mm-dd'),2);
insert into bookEnrol values(3,2,to_date('2009-01-14','yyyy-mm-dd'),1);
insert into bookEnrol values(4,1,to_date('2009-01-17','yyyy-mm-dd'),1);
insert into bookEnrol values(5,2,to_date('2009-02-14','yyyy-mm-dd'),2);
insert into bookEnrol values(6,2,to_date('2009-02-15','yyyy-mm-dd'),1);
insert into bookEnrol values(7,3,to_date('2009-02-18','yyyy-mm-dd'),1);
insert into bookEnrol values(8,3,to_date('2009-02-19','yyyy-mm-dd'),2);
/*方案一*/
select a.id,a.name,b.dependdate from book a,bookenrol b where
a.id=b.bookid
and
b.dependdate in(select max(dependdate) from bookenrol group by bookid )
and b.state=1
/*方案二*/
select k.id,k.name,a.dependdate
from bookenrol a, BOOK k
where a.id in (select max(b.id) from bookenrol b group by b.bookid)
and a.state = 1
and a.bookid = k.id;
