From: Christopher Browne <cbbrowne@acm.org>
To: pgsql-sql@postgresql.org
Subject: Re: User defined types -- Social Security number...
Date: Sun, 29 Feb 2004 23:11:31 -0500
Message-ID: <m37jy5ryto.fsf@wolfe.cbbrowne.com> (raw)
References: <c16fu8$2ro4$1@news.hub.org>
<200402221132.50311.josh@agliodbs.com>
<c1bih1$1r8$1@news.hub.org>
<20040301031716.GB4046@michaelchaney.com>
The world rejoiced as mdchaney@michaelchaney.com (Michael Chaney) wrote:
> Look, you're thinking way too hard on this. An SSN is a 9-digit number,
> nothing more. There are some 9-digit numbers which aren't valid SSN's,
> and you might want to get fancy and create a constraint for that.
>
> Regardless, you are making a *major* mistake of confusing data
> storage with rendering. It is common to *render* an SSN as
> xxx-xx-xxxx and its cousin the FETID (Federal Employers Tax ID) as
> xx-xxxxxxx. To store the dashes makes no sense. They're in the
> same place each time, it's wasted data.
>
> Store the SSN as an "integer". When you begin to think about this
> correctly, the "leading zeros" problem disappears since that is also a
> *rendering* issue.
Well put.
The one thing that is a bit unfortunate is that 32 bit ints aren't
quite big enough for this. You need 1 extra digit :-(.
> When you pull the data out, either fix it up in your programming
> language to the format that you wish, or use the to_char function as
> shown above in your select statements.
Using a view to hide the "physical" representation is also an idea.
A full scale type definition could make for an even more efficient
approach that makes the implementation appear invisible.
> To help you think about this whole issue, consider the timestamp
> datatype. Timestamps are stored as a Julian date internally. I
> suspect that they use a double-floating point as the actual format,
> but regardless the point is that it's a number. Rather than storing
Actually, it's an "int64"; a 64 bit integer, on platforms that support
that type. It's a "double" only on platforms that do not support that
type.
> It's easier to use that as a basic format from which we can render
> it in any way we wish.
Indeed.
--
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Subject: Re: User defined types -- Social Security number...
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