周末,快下班的时候上csdn忽悠几贴,感觉这个有意思,就记录一下自己写的方法。
原问题:
根据分类,每类随机抽取N个(N对每个分类都不一样)
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
根据计划播放类别表,从音乐分类表中随机选出对应类的某一首歌,以生成播放队列(最好重复性少,或没有重复)
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
--实际情况音乐分类表约有9万条记录,计划播放类别表约有800条记录
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
--音乐分类表
create table music_category(id int identity(1,1),musicid int,songcategoryid int)
--计划播放类别表
create table plans(id int identity(1,1),songcategoryid int)
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
insert music_category(musicid,songcategoryid)
select 1,1
union all select 2,1
union all select 3,1
union all select 4,1
union all select 5,1
union all select 6,1
union all select 7,2
union all select 8,2
union all select 9,2
union all select 10,2
union all select 11,3
union all select 12,3
union all select 13,4
union all select 14,4
union all select 15,5
union all select 16,5
union all select 17,5
union all select 18,5
union all select 19,6
union all select 20,7
union all select 21,8
union all select 22,8
union all select 23,8
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
select * from music_category order by songcategoryid,musicid
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
insert plans(songcategoryid)
select 1
union all select 1
union all select 3
union all select 1
union all select 5
union all select 6
union all select 4
union all select 2
union all select 1
union all select 4
union all select 2
union all select 2
union all select 7
union all select 4
union all select 7
union all select 2
union all select 5
union all select 5
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
select * from plans order by id
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
--drop table plans,music_category
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
自己写的一条解决方法:
楼主可以参考一下方法,该方法有时候会重复,有时间我再优化优化(借用Yang_(扬帆破浪) ( ) 大哥的建表数据):
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
--音乐分类表
SET NOCOUNT ON
create table music_category(id int identity(1,1),musicid int,songcategoryid int)
--计划播放类别表
create table plans(id int identity(1,1),songcategoryid int)
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
insert music_category(musicid,songcategoryid)
select 1,1
union all select 2,1
union all select 3,1
union all select 4,1
union all select 5,1
union all select 6,1
union all select 7,2
union all select 8,2
union all select 9,2
union all select 10,2
union all select 11,3
union all select 12,3
union all select 13,4
union all select 14,4
union all select 15,5
union all select 16,5
union all select 17,5
union all select 18,5
union all select 19,6
union all select 20,7
union all select 21,8
union all select 22,8
union all select 23,8
insert plans(songcategoryid)
select 1
union all select 1
union all select 3
union all select 1
union all select 5
union all select 6
union all select 4
union all select 2
union all select 1
union all select 4
union all select 2
union all select 2
union all select 7
union all select 4
union all select 7
union all select 2
union all select 5
union all select 5
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
DECLARE @EXECUTE_SQL nvarchar(4000)
--构造结果表
SELECT *,CAST(NULL as int) musicid INTO #T FROM plans
SELECT MIN([ID]) AS [ID] INTO #ID FROM #T WHERE musicid IS NULL GROUP BY songcategoryid
WHILE EXISTS(SELECT 1 FROM #ID)
BEGIN
--分组统计,根据各组随机得到音乐UPDATE到结果表#T中
UPDATE A SET A.musicid=B.musicid
FROM #T AS A INNER JOIN
(SELECT songcategoryid,MIN(musicid) AS musicid FROM music_category AS A1
WHERE
A1.musicid in(SELECT top 1 B1.musicid FROM music_category AS B1 WHERE
B1.songcategoryid=A1.songcategoryid
AND NOT EXISTS(SELECT 1 FROM #T AS C1 WHERE C1.musicid=B1.musicid)
ORDER BY NEWID() DESC)
AND NOT EXISTS(SELECT 1 FROM #T AS B1 WHERE B1.musicid=A1.musicid)
GROUP BY songcategoryid
) AS B ON B.songcategoryid=A.songcategoryid AND A.musicid IS NULL
WHERE A.ID IN(SELECT MIN([ID]) FROM #T WHERE musicid IS NULL GROUP BY songcategoryid)
--这里主要是考虑分组后UPDATE后,可能还所有一些(必定存在重复的)音乐
--这一段不用考虑唯一性,只要随机就ok。
--不要下面语句可能会死循环
IF NOT EXISTS(SELECT 1 FROM #ID AS A WHERE NOT EXISTS(SELECT 1 FROM #T AS B WHERE B.[id]=A.[ID] AND B.musicid IS NULL))
BEGIN
PRINT 1
UPDATE A SET A.musicid=B.musicid
FROM #T AS A INNER JOIN
(SELECT songcategoryid,MIN(musicid) AS musicid FROM music_category AS A1
WHERE A1.musicid in(SELECT top 1 B1.musicid FROM music_category AS B1 WHERE
B1.songcategoryid=A1.songcategoryid
ORDER BY NEWID() DESC)
GROUP BY songcategoryid
) AS B ON B.songcategoryid=A.songcategoryid AND A.musicid IS NULL
WHERE A.ID IN(SELECT MIN([ID]) FROM #T WHERE musicid IS NULL GROUP BY songcategoryid)
END
TRUNCATE TABLE #ID
INSERT INTO #ID SELECT MIN([ID]) FROM #T WHERE musicid IS NULL GROUP BY songcategoryid
END
SELECT * FROM #T --ORDER BY songcategoryid
DROP TABLE #T,#ID
drop table plans,music_category
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedBlockStart.gif)
/**//*
结果:
id songcategoryid musicid
1 1 1
2 1 5
3 3 11
4 1 2
5 5 16
6 6 19
7 4 13
8 2 8
9 1 3
10 4 14
11 2 7
12 2 10
13 7 20
14 4 14
15 7 20
16 2 9
17 5 15
18 5 17
![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
*/
![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
随机出现重复的可能性小,当然还可以优化一下。
有时间再看怎么样优化,把随机性控制到最小。