Re: Discussion wanted: 'Trigger on Delete' cascade.
От | Pierre-Frédéric Caillaud |
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Тема | Re: Discussion wanted: 'Trigger on Delete' cascade. |
Дата | |
Msg-id | opsbuhzpp3cq72hf@musicbox обсуждение исходный текст |
Ответ на | Discussion wanted: 'Trigger on Delete' cascade. (R.Welz <linuxprodukte@gmx.de>) |
Список | pgsql-general |
Display all headersTo: "R.Welz" <linuxprodukte@gmx.de> Subject: Re: [GENERAL] Discussion wanted: 'Trigger on Delete' cascade. Date: Wed, 28 Jul 2004 13:24:26 +0200 From: Pierre-Frédéric Caillaud <lists@boutiquenumerique.com> Organization: La Boutique Numérique From what you say, your do not need a link table. A link table is useful to link several items of a table to several items of another table (many-to- many relationship). Example : items and categories. 1- An item belongs to a category No need for a link table. table categories ( id serial primary key ); table items ( category_id integer references categories( id ) on delete cascade ); 1- An item belongs to several categories table categories ( id serial primary key ); table items ( id serial primary key ); table links ( category_id integer references categories( id ) on delete cascade, item_id integer references items( id ) on delete cascade, ); In this case you do need a link table. You also need triggers to delete items when - a link is deleted from the links table - no more links to this item exist which is, in fact, reference counting.
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