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Posted by Erland Sommarskog on 02/02/07 10:15
(andylole@gmail.com) writes:
> I've got a db table containing 5 columns(excluding id) consisting of
> 1.) First Half of a UK postcode
> 2.) Town name to which postcode belongs
> 3.) Latitude of Postcode
> 4.) Longitude of Postcode
> 5.) Second Part of the Postcode
>
> I want to select columns 1,2,3 and 4, but once only. There are often
> several entries where 1 and 2 are the same but 3 and 4 are different
> i.e.
> WA1 Bewsey and Whitecross 53.386492 -2.596847
> WA1 Bewsey and Whitecross 53.388203 -2.590961
> WA1 Bewsey and Whitecross 53.388875 -2.598504
> WA1 Fairfield and Howley 53.388455 -2.581701
> WA1 Fairfield and Howley 53.396117 -2.571789
>
> My current query is
> SELECT DISTINCT Postcode, Town, latitude, longitude
> FROM Postcode
> WHERE Postcode.Postcode = 'wa1'
> ORDER BY Postcode, Town
>
> However as latitude and longitude differ on each line DISTINCT does
> not do what I'm looking for.
> Can anybody suggest a way changing the query to just give the first
> instance of each Postcode/Town combo?
A simple way out would be:
SELECT Postcode, Town, AVG(latitude), AVG(longitude)
FROM Postcode
GROUP BY Postcode, Town
Of course, this yield data that is not in the table at all, but it's a
reasonable assumption that the different lat/long values are in the same
proximity. And if they are not, you have a much bigger problem anyway.
--
Erland Sommarskog, SQL Server MVP, esquel@sommarskog.se
Books Online for SQL Server 2005 at
http://www.microsoft.com/technet/prodtechnol/sql/2005/downloads/books.mspx
Books Online for SQL Server 2000 at
http://www.microsoft.com/sql/prodinfo/previousversions/books.mspx
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