Re: Generic design: char vs varchar primary keys

2011/8/3 Raj Mathur (राज माथुर) <raju@linux-delhi.org>:
> Hi,
>
> Can you point me to any pages that explain the difference between using,
> say CHAR(8) vs VARCHAR(8) as the primary key for a table?  Is there any
> impact on the database in terms of:
>
> - Speed of indexed retrieval
> - Speed of join from a referencing table
> - Storage (I presume VARHAR(8) would have a slight edge, in general)
> - Any other issue

The docs have good info about the differences between these types:
http://www.postgresql.org/docs/current/static/datatype-character.html

I suspect the tiny size differences between char(8) and varchar(8) are
going to be negligible. In fact, this post talks precisely about this
concern, and more: http://www.depesz.com/index.php/2010/03/02/charx-vs-varcharx-vs-varchar-vs-text/

Personally I'd be most worried about the different semantics of the
types (i.e. treatment of trailing spaces), and perhaps the ease of
expanding the length constraint in the future.

Josh