Message-ID: <52602BF9.7020403@archidevsys.co.nz>
Date: Fri, 18 Oct 2013 07:27:05 +1300
From: Gavin Flower <GavinFlower@archidevsys.co.nz>
Organization: ArchiDevSys
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To: Gary Stainburn <gary.stainburn@ringways.co.uk>,
 "pgsql-sql@postgresql.org" <pgsql-sql@postgresql.org>
Subject: Re: Advice - indexing on varchar fields where only last x characters
 known
References: <201310171220.44550.gary.stainburn@ringways.co.uk>
In-Reply-To: <201310171220.44550.gary.stainburn@ringways.co.uk>
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On 18/10/13 00:20, Gary Stainburn wrote:
> I have a problem with a field that appears on a number of my tables.
>
> The field is the Vehicle Identification Number. Every vehicle has one and it
> uniquely identifies that vehicle.
>
> Traditionally this was a 11 character string but a number of years ago was
> extended to 17 characters by adding a 6 character prefix.
>
>
> The problem that I have is that these VIN numbers are provided by a number of
> data systems including manufacturer feeds, logistics companies as well as
> internal systems. Some use the full 17 character string while others only use
> the last 11.
>
> On top of this, my users are used to only having to type the last 6 characters
> for speed and usability reasons.
>
> However, it means that every time I'm trying to connect various tables up
> using foreign keys or doing searches I have to make allowences for this which
> means I'm using things like substring, like, regex etc. all of which are very
> slow.
>
> Can anyone suggest a better / more efficient way of handling these.
>
> Gary
>
>
Use 2 fields, one for the 6 character prefix, and the other for the 
original 11 digits.

Search for the 6 character prefix, or a null prefix AND the first 6 
characters of the 11 digit field.

It might be better to have a string for the prefix and make it blank 
rather than null, when nothing is entered there.


Cheers,
Gavin


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