On 3/31/13, Tim Uckun <timuckun@gmail.com> wrote:
> Consider the following scenario.
>
> I have a typical tagging structure. There is a table called tags, there is
> a table called taggings. The taggings table acts as a many to many join
> table between the taggers and the tags.
>
> The tags table has two fields id and tag. id is a serial data type.
>
> The taggings has a tag_id field along with the context, tagger_id etc.
>
> I don't think there is even one query in this scenario which does not join
> the taggings table to the tags table so I am wondering if there is any
> advantage at all of having that id field in the tags table. Why shouldn't I
> just put the tag itself as the primary key? The tags are quite short so if
> pg is smart about it I would guess they would take up less space than an
> integer in some cases.
>
> I guess the same scenario happens in many of my lookup tables. I have all
> these tables with just two fields in them. id field and then some varchar
> field. Then every time I want to display that record I join with five
> other tables so I can look up all the associated lookup tables and display
> the text value to the user.
>
> Given that you can still set foreign keys and cascade commands to adjust
> child records either way the tables would be properly normalized so I am
> wondering what I am gaining by using these serial ID fields.
You can. Arguably, if the natural key is relatively short and consists of only
one column E.F. Codd would probably have encourage you to use it. I'd leave the
serial column for convenience of identifying individual records on the command
line, especially if the varchar can store characters that are not easily typed
in a console.
As for the primary key being a 'natural key' vs. a 'synthetic' one,
that's a huge debate akin to emacs vs. vi. Depending on your situation, there's
nothing wrong with using natural keys. It is discussed at length and
in some cases encouraged here::
http://database-programmer.blogspot.com/2008/01/database-skills-sane-approach-to.html
-Modulok-