Database Design and the use of non-numeric Primary

Question

I'm currently in the process of designing the database tables for a customer & website management application. My question is in regards to the use of primary keys as functional parts of a table (and not assigning "ID" numbers to every table just because).

For example, here are four related tables from the database so far, one of which uses the traditional primary key number, the others which use unique names as the primary key:

--
-- website
--
CREATE TABLE IF NOT EXISTS `website` (
  `name` varchar(126) NOT NULL,
  `client_id` int(11) NOT NULL,
  `date_created` timestamp NOT NULL default CURRENT_TIMESTAMP,
  `notes` text NOT NULL,
  `website_status` varchar(26) NOT NULL,
  PRIMARY KEY  (`name`),
  KEY `client_id` (`client_id`),
  KEY `website_status` (`website_status`),
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

--
-- website_status
--
CREATE TABLE IF NOT EXISTS `website_status` (
  `name` varchar(26) NOT NULL,
  PRIMARY KEY  (`name`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
INSERT INTO `website_status` (`name`) VALUES
('demo'),
('disabled'),
('live'),
('purchased'),
('transfered');

--
-- client
--
CREATE TABLE IF NOT EXISTS `client` (
  `id` int(11) NOT NULL auto_increment,
  `date_created` timestamp NOT NULL default CURRENT_TIMESTAMP,
  `client_status` varchar(26) NOT NULL,
  `firstname` varchar(26) NOT NULL,
  `lastname` varchar(46) NOT NULL,
  `address` varchar(78) NOT NULL,
  `city` varchar(56) NOT NULL,
  `state` varchar(2) NOT NULL,
  `zip` int(11) NOT NULL,
  `country` varchar(3) NOT NULL,
  `phone` text NOT NULL,
  `email` varchar(78) NOT NULL,
  `notes` text NOT NULL,
  PRIMARY KEY  (`id`),
  KEY `client_status` (`client_status`)
) ENGINE=InnoDB  DEFAULT CHARSET=latin1 AUTO_INCREMENT=4 ;

--
-- client_status
---
CREATE TABLE IF NOT EXISTS `client_status` (
  `name` varchar(26) NOT NULL,
  PRIMARY KEY  (`name`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

INSERT INTO `client_status` (`name`) VALUES
('affiliate'),
('customer'),
('demo'),
('disabled'),
('reseller');

As you can see, 3 of the 4 tables use their 'name' as the primary key. I know that these will always be unique. In 2 of the cases (the *_status tables) I am basically using a dynamic replacement for ENUM, since status options could change in the future, and for the 'website' table, I know that the 'name' of the website will always be unique.

I'm wondering if this is sound logic, getting rid of table ID's when I know the name is always going to be a unique identifier, or a recipe for disaster? I'm not a seasoned DBA so any feedback, critique, etc. would be extremely helpful.

Thanks for taking the time to read this!

Answer 1

When making natural PRIMARY KEY's, make sure their uniqueness is under your control.

If you're absolutely sure you will never ever have uniqueness violation, then it's OK to use these values as PRIMARY KEY's.

Since website_status and client_status seem to be generated and used by you and only by you, it's acceptable to use them as a PRIMARY KEY, though having a long key may impact performance.

website name seems be under control of the outer world, that's why I'd make it a plain field. What if they want to rename their website?

The counterexamples would be SSN and ZIP codes: it's not you who generates them and there is no guarantee that they won't be ever duplicated.

Answer 2

"If you're absolutely sure you will never ever have uniqueness violation, then it's OK to use these values as PRIMARY KEY's."

If you're absolutely sure you will never ever have uniqueness violation, then don't bother to define the key.

Answer 3

Kimberly Tripp has an Excellent series of blog articles (GUIDs as PRIMARY KEYs and/or the clustering key and The Clustered Index Debate Continues) on the issue of creating clustered indexes, and choosing the primary key (related issues, but not always exactly the same). Her recommendation is that a clustered index/primary key should be:

1. Unique (otherwise useless as a key)
2. Narrow (the key is used in all non-clustered indexes, and in foreign-key relationships)
3. Static (you don't want to have to change all related records)
4. Always Increasing (so new records always get added to the end of the table, and don't have to be inserted in the middle)

Using "Name" as your key, while it seems to satisfy #1, doesn't satisfy ANY of the other three.

Even for your "lookup" table, what if your boss decides to change all affiliates to partners instead? You'll have to modify all rows in the database that use this value.

From a performance perspective, I'm probably most concerned that a key be narrow. If your website name is actually a long URL, then that could really bloat the size of any non-clustered indexes, and all tables that use it as a foreign key.

Answer 4

I would argue that a database that is resistant to corruption, even if it runs a little slower, is better than one that isn’t.

In general, surrogate keys (such as arbitrary numeric identifiers) undermine the integrity of the database. Primary keys are the main way of identifying rows in the database; if the primary key values are not meaningful, the constraint is not meaningful. Any foreign keys that refer to surrogate primary keys are therefore also suspect. Whenever you have to retrieve, update or delete individual rows (and be guaranteed of affecting only one), the primary key (or another candidate key) is what you must use; having to work out what a surrogate key value is when there is a meaningful alternative key is a redundant and potentially dangerous step for users and applications.

Even if it means using a composite key to ensure uniqueness, I would advocate using a meaningful, natural set of attributes as the primary key, whenever possible. If you need to record the attributes anyway, why add another one? That said, surrogate keys are fine when there is no natural, stable, concise, guaranteed-to-be-unique key (e.g. for people).

You could also consider using index key compression, if your DBMS supports it. This can be very effective, especially for indexes on composite keys (think trie data structures), and especially if the least selective attributes can appear first in the index.

Answer 5

There are 2 reasons I would always add an ID number to a lookup / ENUM table:

1. If you are referencing a single column table with the name then you may be better served by using a constraint
2. What happens if you wanted to rename one of the client_status entries? e.g. if you wanted to change the name from 'affiliate' to 'affiliate user' you would need to update the client table which should not be necessary. The ID number serves as the reference and the name is the description.

In the website table, if you are confident that the name will be unique then it is fine to use as a primary key. Personally I would still assign a numeric ID as it reduces the space used in foreign key tables and I find it easier to manage.

EDIT: As stated above, you will run into problems if the website name is renamed. By making this the primary key you will be making it very difficult if not impossible for this to be changed at a later date.

Answer 6

I think I am in agreement with cheduardo. It has been 25 years since I took a course in database design but I recall being told that database engines can more efficiently manage and load indexes that use character keys. The comments about the database having to update thousands of records when a key is changed and on all of the added space being taken up by the longer keys and then having to be transferred across systems, assumes that the key is actually stored in the records and that it does not have to be transferred across systems anyway. If you create an index on a column(s) of a table, I do not think the value is stored in the records of the table (unless you set some option to do so).

If you have a natural key for a table, even if it is changed occassionally, creating another key creates a redundancy that could result in data integrity issues and actually creates even more information that needs to be stored and transferred across systems. I work for a team that decided to store the local application settings in the database. They have an identity column for each setting, a section name, a key name, and a key value. They have a stored procedure (another holy war) to save a setting that ensures it does not appear twice. I have yet to find a case where I would use a setting's ID. I have, however, ended up with multiple records with the same section and key name that caused my application to fail. And yes, I know that could have been avoided by defining a constraint on the columns.