Re: WIP: generalized index constraints
От | Jeff Davis |
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Тема | Re: WIP: generalized index constraints |
Дата | |
Msg-id | 1246895872.28986.36.camel@jdavis обсуждение исходный текст |
Ответ на | Re: WIP: generalized index constraints (David Fetter <david@fetter.org>) |
Ответы |
Re: WIP: generalized index constraints
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Список | pgsql-hackers |
On Mon, 2009-07-06 at 07:30 -0700, David Fetter wrote: > > It would be useful to see a real example of what this can be used > > for. > > Constraints like "these intervals can't overlap" would be one. It's > handy in calendaring applications, for example. Exactly, you already know my use case ;) My goal is a "temporal key", where you can't have overlapping intervals of time, e.g. the constraint "nobody can be two places at the same time". > > I think it will be useful to separate the concepts of a constraint > > from the concept of an index. It seems possible to have a UNIQUE > > constraint that doesn't help at all in locating rows, just in > > proving that the rows are unique. > > Interesting idea. Are you thinking of this in terms of things the > planner can do once it knows a set is all distinct values, or...? I think that's an orthogonal idea. It's a good idea though, I would like the planner to be smarter about those kinds of things. A simple example is that if a table has a non-partial unique constraint anywhere, then "select * from foo union select * from foo" can be transformed into "select * from foo" (eliminating the expensive union). Regards,Jeff Davis
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