On Tue, 2002-12-03 at 09:53, Adler, Stephen wrote:
> Paul and Michael,
[snip]
>
> When I went to fill this table, under psql, psql immediately
> gave me errors saying that magent(masterindex) was being
> filled with identical values. So, is there a way of defining
> an index as part of the create table command, or is this
> a mysql extention? After reading the chapter on Indexs in
Is there a pressing need to have it in only 1 statement?
> the users guide, there is no mention of creating an index
> as part of the create table, but rather an index is
> a separate entity used to aid the select command. Am I
> getting keys and indexes mixed up? (I assume they are
> the same thing....)
Pedanticly, a key and an index are radically different:
- A key describes a set of records.
- with Primary Key, that set must only contain 1 record.
- Foreign Keys describe sets of 1 or more records that
also have a Primary Key of the same value in a seperate
table.
- An index is a method speeding up access to data. Typical
types of indexes are:
- Hashes
- Trees
As you can see, a UNIQUE index (note that I am not describing
how the index works) is perfect for *implementing* primary keys.
Postgres takes a short cut, and implicitly creates a unique
index when you define a primary key.
"Duplicates allows" indexes are used by Postgres to implement
foreign keys, but, as you see from magent(masterindex), they
are usually used "just" to speed access.
Ron
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| Ron Johnson, Jr. mailto:ron.l.johnson@cox.net |
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| "they love our milk and honey, but preach about another |
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