What is the best way to store single non-repeating data to a database?

Question

What is best practice for storing data in a database which ever only requires a single entry. An example would be configuration data which relates to the entire application/website. Is it common to create a table for this which has only a single entry?

I'm asking under the context of a MongoDB database though I think the question is also valid for SQL databases.

Answer 1

An example of an auxiliary table commonly found in databases would be called Constants and may hold such values of pi, the idea begin that all applications using the database are required to use the same scale and precision. In standard SQL, to ensure they is at most one row e.g. (from Joe Celko):

CREATE TABLE Constants
(
 lock CHAR(1) DEFAULT 'X' NOT NULL PRIMARY KEY, 
 CHECK (lock = 'X'),
 pi FLOAT DEFAULT 3.142592653 NOT NULL,
 e FLOAT DEFAULT 2.71828182 NOT NULL,
 phi FLOAT DEFAULT 1.6180339887 NOT NULL, 
 ...
);

Because mySQL doesn't support CHECK constraint then a trigger is required to achieve the same.

Answer 2

A table would be fine, no reason why not to use it just because it will have only one row.

I just had the weirdest idea (I wouldn't implement it but for some reason I thought of that). You can create a hard-coded view like this:

create view myConfigView 
as
select 'myConfigvalue1' as configValue1, 'myConfigvalue2' as configValue2

and do select * from myConfigView :)

but again, no reason why not to use a table just because it will have only one row