Join returns more than one row, Post code regular expressions

Hi,

I trying to write a select statement that will return each of my sales
men a region code based on a table of post codes using wildcards... eg.
MK1 1AA would be matched in the region code table to MK1%

SELECT     dn.DEALER_CODE, dn.NAME AS DNAME, rc.REGION_ID,
rc.POST_CODE, dn.POSTAL_CODE
FROM         REGIONAL_CODES rc CROSS JOIN
DEALER_NAW dn
WHERE     (dn.POSTAL_CODE LIKE rc.POST_CODE)

The above statement works BUT there are some post code areas such as
our friends in Milton Keynes that are split into two regions...  eg MK1
is region id 2 and MK10 is region 3.

So a dealer with post code MK10 1AA would be matched to both rows
returning duplicates
POST_CODE      REGION_ID
MK1%                2
MK10%              3

I think the answer would lie in a subquery which returns the ID of the
region with the longest length of the postcode match (e.g.
len(POST_CODE) for the rc table...  return only the MAX....

any ideas????

Any help muchos appreciated, and I apologies now for the naming of the
dealers name as a reserve word... not me!

Ct

cheesey_toastie  wrote:
> Hi,
>
> I trying to write a select statement that will return each of my sales
> men a region code based on a table of post codes using wildcards... eg.
>  MK1 1AA would be matched in the region code table to MK1%
>
> SELECT     dn.DEALER_CODE, dn.NAME AS DNAME, rc.REGION_ID,
> rc.POST_CODE, dn.POSTAL_CODE
> FROM         REGIONAL_CODES rc CROSS JOIN
>                       DEALER_NAW dn
> WHERE     (dn.POSTAL_CODE LIKE rc.POST_CODE)
>
> The above statement works BUT there are some post code areas such as
> our friends in Milton Keynes that are split into two regions...  eg MK1
> is region id 2 and MK10 is region 3.
>
> So a dealer with post code MK10 1AA would be matched to both rows
> returning duplicates
> POST_CODE      REGION_ID
> MK1%                2
> MK10%              3
>
> I think the answer would lie in a subquery which returns the ID of the
> region with the longest length of the postcode match (e.g.
> len(POST_CODE) for the rc table...  return only the MAX....
>
> any ideas????
>
> Any help muchos appreciated, and I apologies now for the naming of the
> dealers name as a reserve word... not me!
>
> Ct

Hi Ct,

I think it would be along the lines of:

SELECT     dn.DEALER_CODE, dn.NAME AS DNAME, rc.REGION_ID,
rc.POST_CODE, dn.POSTAL_CODE
FROM         REGIONAL_CODES rc CROSS JOIN
DEALER_NAW dn
WHERE     (dn.POSTAL_CODE LIKE rc.POST_CODE) and not exists (select *
from REGIONAL_CODES rc2 where dn.POSTAL_CODE LIKE rc2.POST_CODE and
LEN(rc2.POSTAL_CODE) > LEN(rc.POSTAL_CODE))

Damien

Hi Damien,

I was first initially dubious that it would work where the post code
matched three different rows e.g.

If postal_code = MK111 1AA ....
MK%
MK1%
MK11%

But it does, and a quick read of
http://www.techonthenet.com/sql/exists.php explained it.
Thanks for that!

Below is the code with the minor corrections of the field names for
anyone following the post...
SELECT     dn.DEALER_CODE, dn.NAME AS DNAME, rc.REGION_ID,
rc.POST_CODE, dn.POSTAL_CODE
FROM         REGIONAL_CODES rc CROSS JOIN
DEALER_NAW dn
WHERE     (dn.POSTAL_CODE LIKE rc.POST_CODE) AND (NOT EXISTS
(SELECT     *
FROM          REGIONAL_CODES rc2
WHERE      dn.POSTAL_CODE LIKE
rc2.POST_CODE AND LEN(rc2.POST_CODE) > LEN(rc.POST_CODE)))

ct