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数据库12（游标）

ds 2025/5/1 6:30:19

游标语法

declare c1 cursor for
select title from titles

--定义一个游标c1，确定游标对应的列是titles表的title列，游标可以对应多个列

declare @bname varchar(50)

--声明变量

open c1

--初始化，开始使用游标
fetch next from c1
into @bname

--初始化游标c1到i=0，即起始位置，把游标对应列的值放入变量中，用作输出

while @@FETCH_STATUS=0

--判断游标状态，是否到最后一行
begin
print 'the name of the book is '+@bname

--对每行做数据做相应操作
fetch next from c1
into @bname

--完成操作后，游标后移，再次把游标对应行的该列值放入变量，重复直到游标到最后一列
end

close c1 --关闭游标
deallocate c1 --销毁游标

practice

first：多个变量，聚合函数输出，返回多个字符串

declare b cursor for
select title_id from titleauthor
declare @titleid1 varchar(50),@sum1 int,@sum2 int,@sum3 int
open b
fetch next from b
into @titleid1
while @@FETCH_STATUS=0
begin
set @sum1=(select count(*) from sales where title_id=@titleid1 and ord_date between '1992-1-1' and '1992-12-30')
set @sum2=(select count(*) from sales where title_id=@titleid1 and ord_date between '1993-1-1' and '1993-12-30')
set @sum3=(select count(*) from sales where title_id=@titleid1 and ord_date between '1994-1-1' and '1994-12-30')
print @titleid1+' '+cast(@sum1 as varchar(10))+' '+cast(@sum2 as varchar(10))+' '+cast(@sum3 as varchar(10))
fetch next from b
into @titleid1
end
close b
deallocate b

second：多个变量，返回表

declare c cursor for
select title_id from titleauthor
declare @titleid2 varchar(50),@asum1 int,@asum2 int,@asum3 int
create table #temptable(
titleid varchar(100),
count92 int,
count93 int,
count94 int)
open c
fetch next from c
into @titleid2
while @@FETCH_STATUS=0
begin
set @asum1=(select count(*) from sales where title_id=@titleid2 and ord_date between '1992-1-1' and '1992-12-30')
set @asum2=(select count(*) from sales where title_id=@titleid2 and ord_date between '1993-1-1' and '1993-12-30')
set @asum3=(select count(*) from sales where title_id=@titleid2 and ord_date between '1994-1-1' and '1994-12-30')
insert into #temptable values(@titleid2,@asum1,@asum2,@asum3)
fetch next from c into @titleid2
end
close c
deallocate c