Is there a standard for storing normalized phone numbers in a database?

Question

What is a good data structure for storing phone numbers in database fields? I\'m looking for something that is flexible enough to handle international numbers, and also som

Answer 1

Here's my proposed structure, I'd appreciate feedback:

The phone database field should be a varchar(42) with the following format:

CountryCode - Number x Extension

So, for example, in the US, we could have:

1-2125551234x1234

This would represent a US number (country code 1) with area-code/number (212) 555 1234 and extension 1234.

Separating out the country code with a dash makes the country code clear to someone who is perusing the data. This is not strictly necessary because country codes are "prefix codes" (you can read them left to right and you will always be able to unambiguously determine the country). But, since country codes have varying lengths (between 1 and 4 characters at the moment) you can't easily tell at a glance the country code unless you use some sort of separator.

I use an "x" to separate the extension because otherwise it really wouldn't be possible (in many cases) to figure out which was the number and which was the extension.

In this way you can store the entire number, including country code and extension, in a single database field, that you can then use to speed up your queries, instead of joining on a user-defined function as you have been painfully doing so far.

Why did I pick a varchar(42)? Well, first off, international phone numbers will be of varied lengths, hence the "var". I am storing a dash and an "x", so that explains the "char", and anyway, you won't be doing integer arithmetic on the phone numbers (I guess) so it makes little sense to try to use a numeric type. As for the length of 42, I used the maximum possible length of all the fields added up, based on Adam Davis' answer, and added 2 for the dash and the 'x".