Re: RI
От | Jean-Yves F. Barbier |
---|---|
Тема | Re: RI |
Дата | |
Msg-id | 20100624133945.4727eb43@anubis.defcon1 обсуждение исходный текст |
Ответ на | Re: RI (Tom Lane <tgl@sss.pgh.pa.us>) |
Список | pgsql-novice |
Le Thu, 24 Jun 2010 00:48:18 -0400, Tom Lane <tgl@sss.pgh.pa.us> a écrit : > Jasen Betts <jasen@xnet.co.nz> writes: > > On 2010-06-24, Jean-Yves F. Barbier <12ukwn@gmail.com> wrote: > >> does a Referential Integrity toward a table also acts like an index, or > >> am I obliged to create this index? > > > The RI does not create any indices. > > There is no requirement to create an index. > > In most cases creating an index at one or both ends or the reference > > is a good idea. > > Well, it's a little bit more complicated than that. A foreign key > constraint can only be created when the referenced (primary key) column > has a unique or primary key constraint. In Postgres, a unique/PK > constraint always has an associated index. So you're already guaranteed > an index on that end of the FK. What will not be present, unless you > create it, is an index on the referencing column. It often is a good > idea to create that index too, but there are some cases where such an > index isn't worth its maintenance overhead. You will want such an index > if you often change or delete entries in the referenced column. If you > seldom do that, and don't often issue queries on the referencing column, > then maybe you don't need that index. This is crystal clear :) Thanks Tom JY -- Sure, and of course I would vote for a woman for president! Quite naturally, we wouldn't have to pay her so much.
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