foreign keys?

[alaios]

Can u tell me why when i want to create a foreign key....i have to create an index for the attribute?

[raf]

It's a performance issue.

An indexed field can be searched much faster on. The fields of a primary key - foreign key relationship should both be indexed, because the joining will then be a lott quicker. The indexpages then maintain a 'key' to the datapages that need to be used to find the corresponding rows, so looking up the fields from the joined records, will be much faster.