关于数据库实验一、二和数据库的创建请参考此处
什么叫游标？游标（cursor）是系统为用户开设的一个数据缓冲区，存放SQL语句的执行结果。每个游标区都有一个名字,用户可以用SQL语句逐一从游标中获取记录，并赋给主变量，交由主语言进一步处理。
游标可以类比于C语言文件中的指针，可以根据需要使得选择对应的行。
游标的生命周期包含有五个阶段：声明游标、打开游标、读取游标数据、关闭游标、释放游标。
这些都是固定的格式，对于游标使用还算是比较常规的。
声明游标：
declare st_cursor cursor
for select colum from table where ...
打开游标：
open st_cursor
读取游标
fetch next from into @你的变量
关闭游标
close st_cursor
释放游标
deallocate st_cursor
本次实验内容是实验三+《数据库原理及应用》书P199 第12-14习题
-- Test3-1
use Library2128
select
出版社,cast(cast(cast(count(出版社) as decimal(4,1))/cast((select count(*)
from
book2128) as decimal(4,1))*100 as decimal(4,1)) as varchar(5)) +'%' 百分比,
case
when cast(count(出版社)as decimal(4,1)) /cast((select count(*)from book2128) as decimal(4,1))>0.5 then '很高'
when cast(count(出版社)as decimal(4,1)) /cast((select count(*)from book2128) as decimal(4,1))>0.3 then '较高'
when cast(count(出版社)as decimal(4,1)) /cast((select count(*)from book2128) as decimal(4,1))>0.1 then '一般'
when cast(count(出版社)as decimal(4,1)) /cast((select count(*)from book2128) as decimal(4,1))<0.1 then '较低'
end 比例
from book2128
group by 出版社
order by cast(count(出版社) as decimal(4,1))/cast((select count(*)from book2128) as decimal(4,1))
-- Test3-2
select
出版社,cast(cast(cast(count(出版社) as decimal(4,1))/cast((select count(*)
from
book2128) as decimal(4,1))*100 as decimal(4,1)) as varchar(5)) +'%' 百分比,
case
when cast(count(出版社)as decimal(4,1)) /cast((select count(*)from book2128) as decimal(4,1))>0.5 then '很高'
when cast(count(出版社)as decimal(4,1)) /cast((select count(*)from book2128) as decimal(4,1))>0.3 then '较高'
when cast(count(出版社)as decimal(4,1)) /cast((select count(*)from book2128) as decimal(4,1))>0.1 then '一般'
when cast(count(出版社)as decimal(4,1)) /cast((select count(*)from book2128) as decimal(4,1))<0.1 then '较低'
end 比例
from book2128
group by 出版社
order by cast(count(出版社) as decimal(4,1))/cast((select count(*)from book2128) as decimal(4,1))
desc
-- Test3-3
declare @bno char(20),@percent char(20),@price int
declare st_cursor cursor
for select distinct book2128.图书名,book2128.定价
from book2128
print 'BOOK Evaluate'
print '---------------------------------'
open st_cursor
fetch next from st_cursor into @bno,@price
while @@FETCH_STATUS=0
begin
set @percent= case
when @price > 50 then 'A'
when @price > 30 then 'B'
when @price > 20 then 'C'
when @price > 10 then 'D'
else 'E'
end
print @bno+' '+@percent
fetch next from st_cursor into @bno,@price
end
close st_cursor
deallocate st_cursor
go
-- Test3-4
declare @pub char(20),@percent decimal(4,1)
declare st_cursor cursor
for select distinct t1.出版社,cast(借阅数*总数 as decimal(4,1)) 借出率
from
(
select count(*) 总数,bk.出版社
from book2128 bk
group by bk.出版社
) t1,
(
select bk.出版社,count(bor.图书编号) 借阅数
from
borrow2128 bor,book2128 bk
where bor.图书编号=bk.图书编号
group by bk.出版社
) t2
where t1.出版社=t2.出版社
open st_cursor
fetch next from st_cursor into @pub,@percent
print '出版社 借出率'
print '----------------------------'
while @@FETCH_STATUS=0
begin
print @pub+' '+(CAST(@percent As char(5)))+'%'
fetch next from st_cursor into @pub,@percent
end
close st_cursor
deallocate st_cursor
go
-- P199-12
set nocount on
declare @sclass nvarchar(10),@savg float
declare st_cursor cursor
for select c.课程名,avg(s.分数)
from course2128 c,score2128 s
where c.课程号=s.课程号
group by (c.课程名)
open st_cursor
fetch next from st_cursor into @sclass,@savg
print 'class Avg'
print '-------------'
while @@fetch_status=0
begin
print cast(@sclass as nvarchar(8))+' '+
cast(@savg as nvarchar(10))
fetch next from st_cursor into @sclass,@savg
end
close st_cursor
deallocate st_cursor
go
-- P199-13
declare @fs int,@dj nvarchar(2),@sno int,@cno nvarchar(10)
declare st_cursor cursor
for select 学号,课程号,分数
from score2128
where 分数 is not null
open st_cursor
fetch next from st_cursor into @sno,@cno,@fs
print 'NUM CLASS SCORE'
print '-----------------------'
while @@fetch_status=0
begin
set @dj=case
when @fs>=90 then 'A'
when @fs>=80 then 'B'
when @fs>=70 then 'C'
when @fs>=60 then 'D'
else 'E'
end
print cast(@sno as char(8))+' '+@cno+' '+@dj
fetch next from st_cursor into @sno,@cno,@fs
end
close st_cursor
deallocate st_cursor
go
--P199 -14
declare @sclass char(10),@savg float
declare st_cursor cursor
for select st.班号,avg(sc.分数)
from student2128 st,score2128 sc
where st.学号=sc.学号
group by st.班号
open st_cursor
fetch next from st_cursor into @sclass,@savg
print 'Class Score'
print '-----------------'
while @@fetch_status=0
begin
print @sclass+cast(@savg as char(10))
fetch next from st_cursor into @sclass,@savg
end
close st_cursor
deallocate st_cursor
go
