>>> I would imagine that other DBMSes also enforce uniqueness by means of >>> indexes, because it'd be awful darn expensive to enforce the constraint >>> without one; but I'm only guessing here, not having looked. Can anyone >>> point to a real system that enforces unique constraints without an >>> underlying index? > > In Rdb/VMS (which does not use MVCC), PK (and it's alias UNIQUE) > constraints are independent of whether you have a unique index on > the table.
PK is NOT an alias for UNIQUE. Yes it does have the same functional operation but it is technically incorrect to consider them the same. > > Now, 99.44% of the time you will *not* have a PK constraint, but > simply a unique index. Then you have designed your database incorrectly. Sincerely, Joshua D. Drake ---------------------------(end of broadcast)--------------------------- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly -- === The PostgreSQL Company: Command Prompt, Inc. === Sales/Support: +1.503.667.4564 || 24x7/Emergency: +1.800.492.2240 Providing the most comprehensive PostgreSQL solutions since 1997 http://www.commandprompt.com/ Donate to the PostgreSQL Project: http://www.postgresql.org/about/donate PostgreSQL Replication: http://www.commandprompt.com/products/ ---------------------------(end of broadcast)--------------------------- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq