5. 1
データベースシステム論 第 回2016 [ 9 ] 5p.
SELECT * FROM vineyard
WHERE did IN
(SELECT did FROM wine
WHERE price<(SELECT avg(price) FROM wine));
SELECT * FROM vineyard
WHERE EXISTS
(SELECT NULL FROM wine
WHERE vineyard.did = wine.did
AND price<(SELECT avg(price) FROM wine));
SELECT DISTINCT wine.did,district
FROM wine JOIN vineyard
ON wine.did = vineyard.did
WHERE price <(SELECT avg(price) FROM wine));
12. ビューの概念
データベースシステム論 第 回2016 [ 9 ] 12p.
ビュー
wine_list
wid
name
district
price
テーブル
vineyard
did
district
テーブル
wine
wid
name
did
price
概念スキーマ 外部スキーマ
ユーザー
SQL
仮想的なテーブル