Svein wrote:

#
Use a generator to populate the PK, never use
composite primary keys.
#

What's the reason for that?

Whenever I've implemented many to many relationships I've used a composite
primary key - it seems the most natural thing to do. e.g.

Table Person:

1 - Jim
2 - Fred
3 - Bob
4 - Sam

Table Clothes:

1 - Shirt
2 - Trousers
3 - Shoes
4 - Tie

Table Wardrobe (many to many on Person, Clothes)

personkey - clotheskey
1 - 2
1 - 3
2 - 1
2 - 2
3 - 3
3 - 4
4 - 2

Table Wardrobe (many to many on Person, Clothes) with generated key

genkey - personkey - clotheskey
1 - 1 - 2
2 - 1 - 3
3 - 2 - 1
4 - 2 - 2
5 - 3 - 3
6 - 3 - 4
7 - 4 - 2

What's the purpose of the generated key - to query the table (who owns
trousers?) you are going to have to refer to person and clothes. Isn't the
addition of genkey going to make the query statements somewhat convoluted?
Is there a big performance win that makes it worth it?

Have I missed something or misunderstood (I'm not a database expert).

Thanks,

Ray










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