A magazine can have several e-mail addresses, and one e-mail address can belong to several magazines. Well, the e-mail addresses belongs to the publisher but for simplification the e-mail address is linked with the magazine.
So what is really more important is that I don't know, is there a big performance penalty of the sort of "trigger calling another trigger" or would it be noticeable faster if the first trigger does all the checking and decides itself wheather to delete table B.
I think of writing a really large database, so performance is most important, or will there be no noticeable performance hit? It is my first big database.
Thank you Robert
Am 28.07.2004 um 13:24 schrieb Pierre-Frédéric Caillaud:
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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