On Sat, Jan 14, 2006 at 07:28:21PM +0900, Michael Glaesemann wrote: > > On Jan 13, 2006, at 21:42 , Leandro Guimar?es Faria Corcete DUTRA wrote: > > >If you still declare the natural key(s) as UNIQUEs, you have just made > >performance worse. Now there are two keys to be checked on UPDATEs > >and > >INSERTs, two indexes to be updated, and probably a SEQUENCE too. > > For UPDATEs and INSERTs, the "proper" primary key also needs to be > checked, but keys are used for more than just checking uniqueness: > they're also often used in JOINs. Joining against a single integer > I'd think it quite a different proposition (I'd think faster in terms > of performance) than joining against, say, a text column or a > composite key.
a) the optimizer does a really poor job on multi-column index statistics b) If each parent record will have many children, the space savings from using a surrogate key can be quite large c) depending on how you view things, putting actual keys all over the place is denormalized Generally, I just use surrogate keys for everything unless performance dictates something else. -- Jim C. Nasby, Sr. Engineering Consultant [EMAIL PROTECTED] Pervasive Software http://pervasive.com work: 512-231-6117 vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461 ---------------------------(end of broadcast)--------------------------- TIP 2: Don't 'kill -9' the postmaster
