From: | Bruno Wolff III <bruno(at)wolff(dot)to> |
---|---|
To: | Vivek Khera <khera(at)kcilink(dot)com> |
Cc: | pgsql-general(at)postgresql(dot)org |
Subject: | Re: [ADMIN] Q: Structured index - which one runs faster? |
Date: | 2003-05-23 16:50:20 |
Message-ID: | 20030523165020.GA11094@wolff.to |
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Lists: | pgsql-admin pgsql-general pgsql-performance |
On Fri, May 23, 2003 at 11:09:00 -0400,
Vivek Khera <khera(at)kcilink(dot)com> wrote:
> A related question:
>
> Are any of these indexes redundant:
>
> CREATE UNIQUE INDEX user_list_id_email ON user_list (owner_id,user_email);
> CREATE INDEX user_list_owner_id ON user_list (owner_id);
> CREATE INDEX user_list_oid_created ON user_list (owner_id,user_created);
>
> In particular, is user_list_owner_id redundant to
> user_list_oid_created? Will the latter be used for queries such as
Yes. Any prefix of a multicolumn index can be used for queries. They
(prefixes) won't be usable by foreign key references because even if the
index as a whole is unique, the prefixes won't necessarily be.
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