1

外部キー制約の簡単な例を次に示します。

CREATE TABLE products (
  product_no integer PRIMARY KEY,
  name text,
  price numeric
);

CREATE TABLE orders (
  order_id integer PRIMARY KEY,
  shipping_address text,
  ...
);

CREATE TABLE order_items (
  product_no integer REFERENCES products ON DELETE CASCADE,
  order_id integer REFERENCES orders ON DELETE CASCADE,
  quantity integer,
  PRIMARY KEY (product_no, order_id)
);

商品または注文から行が削除されると、order_items からの参照行も削除されます。

しかし、製品または注文から孤立した行 (order_item を参照していない行) をデータベースで検出して削除することは可能ですか? 十分に簡単に実行できるようにクエリを設定できることはわかっていますが、より大規模で複雑なスキーマでは、大量のクエリになる可能性があります。ON DELETE CASCADE と同様のメカニズムがあるかどうか疑問に思っていますか?

4

1 に答える 1

1

参照カウントのない例を次に示します。

DROP SCHEMA tmp CASCADE;
CREATE SCHEMA tmp ;
SET search_path=tmp;

CREATE TABLE one
    ( id SERIAL NOT NULL PRIMARY KEY
    , name VARCHAR
    );
CREATE TABLE two
    ( id SERIAL NOT NULL PRIMARY KEY
    , name VARCHAR
    );
CREATE TABLE onetwo
    ( one_id INTEGER REFERENCES one(id)
    , two_id INTEGER REFERENCES two(id)
        , PRIMARY KEY(one_id, two_id)
    );
CREATE INDEX onetwo_rev ON onetwo (two_id,one_id);

  -- Populate the tables.
INSERT INTO one(name) select 'One_name_' || gs::text FROM generate_series(1,5) gs ;
INSERT INTO two(name) select 'Two_name_' || gs::text FROM generate_series(1,5) gs ;
INSERT INTO onetwo (one_id, two_id)
SELECT o.id, t.id
FROM one o
JOIN two t ON 1=1
        ;
  -- Remove some random associations between one&two,
  -- and remove any unreferenced records from one and two
DELETE FROM onetwo WHERE random() < 0.7;
DELETE FROM one dd WHERE NOT EXISTS(SELECT * FROM onetwo ot WHERE ot.one_id=dd.id) ;
DELETE FROM two dd WHERE NOT EXISTS(SELECT * FROM onetwo ot WHERE ot.two_id=dd.id) ;

SELECT * FROM onetwo;
SELECT * FROM one;
SELECT * FROM two;

CREATE OR REPLACE FUNCTION check_the_deletes() RETURNS TRIGGER AS $meat$
BEGIN
    DELETE FROM one dd
    WHERE dd.id=OLD.one_id
    AND NOT EXISTS(SELECT * FROM onetwo ot WHERE ot.one_id=dd.id)
       ;
    DELETE FROM two dd
    WHERE dd.id=OLD.two_id
    AND NOT EXISTS(SELECT * FROM onetwo ot WHERE ot.two_id=dd.id)
       ;
    RETURN NEW;
END; $meat$
LANGUAGE plpgsql;

CREATE TRIGGER update_last_sale
    AFTER DELETE ON onetwo
    FOR EACH ROW
    EXECUTE PROCEDURE check_the_deletes()
     ;

SELECT o.name AS name1
        , t.name AS name2
FROM onetwo ot
JOIN one o ON o.id = ot.one_id
JOIN two t ON t.id = ot.two_id
        ;

  -- Delete some random associations
  -- the trigger should also remove any unreferenced rows
  -- from one and two tables.
DELETE FROM onetwo WHERE random() < 0.4;

SELECT o.name AS name1
        , t.name AS name2
FROM onetwo ot
JOIN one o ON o.id = ot.one_id
JOIN two t ON t.id = ot.two_id
        ;
SELECT * FROM one;
SELECT * FROM two;
于 2013-02-27T12:43:08.927 に答える