回答編集履歴
4
kaisetu
test
CHANGED
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@@ -82,6 +82,14 @@
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```
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※解説
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where not existsは相関サブクエリといいます。
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88
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moviesのmidを利用して、サブクエリ内50以下の評価があるmidを
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not existsで反転して評価がないものを抽出しています
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# 検証2
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@@ -111,3 +119,13 @@
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order by avg_rating desc
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```
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※解説
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単純にサブクエリないでmidごとの平均ratingを計算し
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n件以上をhavingで抽出しています
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group by~having構文は最低限覚える必要があるSQLの一つです
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あとはサブクエリとしてmovieに結合しています
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3
調整
test
CHANGED
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@@ -81,3 +81,33 @@
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where mid=t1.mid)
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```
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# 検証2
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サンプル数が少ないのでとりあえず2件以上評価があるもの
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mid=1,2とその平均評価
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```SQL
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select t1.mid,t1.title,t2.avg_rating
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from movies as t1
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inner join (
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select mid,avg(rating) as avg_rating
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from ratings
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group by mid
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having count(*)>=2
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) as t2 on t1.mid=t2.mid
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order by avg_rating desc
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```
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2
調整
test
CHANGED
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@@ -21,3 +21,63 @@
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的なことではないのでしょうか？
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※質問者さんの意向にあわせて不等号を逆にしました
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# 検証1
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ざっくりデータを削ります
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```SQL
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create table movies(mid int primary key,title varchar(100));
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insert into movies values(1,'aaa'),(2,'bbb'),(3,'ccc'),(4,'ddd'),(5,'eee'),(6,'fff');
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create table users(uid int primary key,name varchar(10),age int);
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insert into users values(1,'AAA',30),(2,'BBB',40),(3,'CCC',55),(4,'DDD',60);
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create table ratings(rid int primary key,uid int,mid int,rating int);
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insert into ratings values(1,1,1,10),(2,1,2,20),(3,2,1,15),(4,2,2,20),(5,2,3,12),(6,4,2,30),(7,5,4,20);
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50
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select * from movies as t1
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left join ratings as t2 on t1.mid = t2.mid
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and ratings.uid = users.uid
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and users.age < 50;
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```
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上記50以下のユーザーuid=1,2が評価したタイトルはmid=1,2,3
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評価していないのはmid=4,5,6
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```SQL
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select * from movies as t1 where
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not exists(
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select 1 from ratings as t2
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inner join users as t3 on t2.uid = t3.uid
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and t3.age < 50
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where mid=t1.mid)
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```
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1
chousei
test
CHANGED
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@@ -14,8 +14,10 @@
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14
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and ratings.userid = users.userid
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-
and users.age
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and users.age < 50;
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```
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的なことではないのでしょうか？
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+
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23
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+
※質問者さんの意向にあわせて不等号を逆にしました
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