學(xué)數(shù)學(xué)的時候都知道有交集和差集的概念。
用SQL語句來表示交集和差集的時候會遇到很多小困難，比如條件有重復(fù)，編號有空等等。
最近在處理一些歌曲列表是否有版權(quán)的時候就遇到過這些困難，現(xiàn)在把它們記錄一下：
copyright_songs表是有版權(quán)的歌曲清單 local_songs表是在用的歌曲清單
生成歌曲名和歌手名都相同的交集用如下SQL：
select distinct t2.id,t1.name,t1.singer,t1.id as local_id,t1.company,
t2.company as copyright_company,t2.type
into same_1
from copyright_songs t2,local_songs t1
where (t1.name=t2.name and t1.singer=t2.singer)
如果歌曲名稱里面帶有括號，如:星語心愿（節(jié)奏版）考試,大提示需要去掉歌曲里面括號后再比較.
select * into local_songs_old from local_songs
update local_songs set name=left(name,charindex(’(’,name)-1)
where charindex(’(’,name)>0
drop table same_1
select distinct t2.id,t1.name,t1.singer,t1.id as local_id,t1.company,
t2.company as copyright_company,t2.type
into same_1
from copyright_songs t2,local_songs t1
where (t1.name=t2.name and t1.singer=t2.singer)
顯示歌曲名和歌手名都相同歌曲清單(交集)
select * from same_1
顯示歌曲名和歌手名都相同歌曲清單，用原來帶括號的歌曲名
select distinct t1.id,t2.name,t1.singer,t1.local_id,t1.company,t1.num,t1.type
from same_1 t1,local_songs_old t2
where t1.t1_id=t2.id
找到?jīng)]有版權(quán)對應(yīng)的歌曲列表
顯示編號是否有為空的記錄
select * from local_songs where id is null
select * from same_1 where local_id is null
去掉編號為空的記錄
delete from local_songs where id is null
delete from same_1 where local_id is null
生成本地歌曲表里面沒有版權(quán)的歌曲清單(差集)
select * into no_local_songs from local_songs
where id not in (select local_id from same_1)
顯示本地歌曲表里面沒有版權(quán)的歌曲清單
select * from no_local_songs
沒有版權(quán)的歌曲就要屏蔽起來，不能再使用原來免費(fèi)的互聯(lián)網(wǎng)音樂來贏利了。
用SQL語句來表示交集和差集的時候會遇到很多小困難，比如條件有重復(fù)，編號有空等等。
最近在處理一些歌曲列表是否有版權(quán)的時候就遇到過這些困難，現(xiàn)在把它們記錄一下：
copyright_songs表是有版權(quán)的歌曲清單 local_songs表是在用的歌曲清單
生成歌曲名和歌手名都相同的交集用如下SQL：
select distinct t2.id,t1.name,t1.singer,t1.id as local_id,t1.company,
t2.company as copyright_company,t2.type
into same_1
from copyright_songs t2,local_songs t1
where (t1.name=t2.name and t1.singer=t2.singer)
如果歌曲名稱里面帶有括號，如:星語心愿（節(jié)奏版）考試,大提示需要去掉歌曲里面括號后再比較.
select * into local_songs_old from local_songs
update local_songs set name=left(name,charindex(’(’,name)-1)
where charindex(’(’,name)>0
drop table same_1
select distinct t2.id,t1.name,t1.singer,t1.id as local_id,t1.company,
t2.company as copyright_company,t2.type
into same_1
from copyright_songs t2,local_songs t1
where (t1.name=t2.name and t1.singer=t2.singer)
顯示歌曲名和歌手名都相同歌曲清單(交集)
select * from same_1
顯示歌曲名和歌手名都相同歌曲清單，用原來帶括號的歌曲名
select distinct t1.id,t2.name,t1.singer,t1.local_id,t1.company,t1.num,t1.type
from same_1 t1,local_songs_old t2
where t1.t1_id=t2.id
找到?jīng)]有版權(quán)對應(yīng)的歌曲列表
顯示編號是否有為空的記錄
select * from local_songs where id is null
select * from same_1 where local_id is null
去掉編號為空的記錄
delete from local_songs where id is null
delete from same_1 where local_id is null
生成本地歌曲表里面沒有版權(quán)的歌曲清單(差集)
select * into no_local_songs from local_songs
where id not in (select local_id from same_1)
顯示本地歌曲表里面沒有版權(quán)的歌曲清單
select * from no_local_songs
沒有版權(quán)的歌曲就要屏蔽起來，不能再使用原來免費(fèi)的互聯(lián)網(wǎng)音樂來贏利了。