Question

I’m trying to understand if there are any standard best practice approaches for modelling number ranges in a Relational Database (In this case MySQL) and if this is in fact a sensible thing to do.

I shall explain the task that prompted the question for context.

I’m currently in the process of designing a database which will model the allocation of a pool of Identifiers to Customers.

The pool of potential Identifiers has a range from 0 to about 2^30

A given customer could be allocated any number of Identifiers from a single Identifier to millions in multiple contiguous blocks.

A given Identifier may only be allocated to a single customer (i.e. it is a one to many relationship)

Clearly there will be a Customer table and and an Identifier table containing the Customer key.

The complexity comes with how to model the Identifiers:

Option one would be to have a row represent single identifier. This will result in a potentially huge number of rows in the table, but would make searching for who owns which identifier and if a given identifier is in use trivial.

The second (and I think more promising) option would be to have a row represent a range of values with a minimum and maximum value. This would make queries a bit more complex (I’m assuming the query for checking if an identifier was in use would be to query for ranges with “Minimum lower than X” and a “Maximum higher than X”) but would result in far fewer rows and would likely be easier to manage and update.

I would welcome any views on if this is a good approach and if not if there is an obvious better approach that I am missing.

Answer 1

If the ranges do not intersect, then you may store them as pairs of INT values:

CREATE TABLE customer_range
        (
        customerId INT,
        rgStart INT,
        rgEnd INT,
        PRIMARY KEY (customerId, rgStart),
        UNIQUE KEY (rgStart)
        )

To query the customer a number belongs to, use this:

SELECT  customerId
FROM    customer_range
WHERE   rgStart <= $mynum
        AND rgEnd >= $mynum
ORDER BY
        rgStart DESC
LIMIT 1