How to order by postcode? - sql

Question

I have a small report that needs to be ordered by postcode. How do I do this?
Using ORDER BY Postcode returns
SK1
SK11
SK13
SK2
How can I return
SK1
SK2
SK11
SK13
EDIT
I should really have added more to the question, I am working with postcodes for the whole of the UK, not just ones starting with SK. So some of these postcodes will start with only 1 letter, some with 2. Also, the second part of the postcode is in the column.

Answer 1

Assuming MSSQL, and that your Postcode field follows a consistent pattern of Char(2) + Number, then you could add a computed query column:
postcode_num = convert(int,substring(postcode,3,len(postcode)))
And then use it instead of Postcode for sorting:
order by postcode_num
Results as desired:

Answer 2

Create 2 columns:
1. a VARCHAR for the first part;
2. a TINYINT for the last (numeric) part.
ORDER BY postcode_prefix, postcode_suffix
Source: https://www.sitepoint.com/community/t/order-by-postcode/50042/9

Answer 3

The problem you are facing is that the column you are trying to ORDER BY is of type text and not numeric, therefore SQL will perform the ordering you're seeing. Instead, if you want SQL to order it as if it was a number then you would need to substring the "SK" part of the column, cast the number characters to numeric type and then order by that.
This is what #LONG replied to you in the first comment.

Answer 4

The way I would approach it is to create a couple of generic functions that will strip the alpha or numeric portions from the string before you sort.
In my example the functions are in the fn schema so change this as you require.
ORDER BY fn.StripToAlpha(PostCode), fn.StripToNumeric(PostCode)
There are plenty of examples of these types of functions around, probably more efficient than the ones I wrote but below is the code to produce the ones I use.
CREATE FUNCTION [fn].[StripToAlpha]
(
#inputString nvarchar(4000)
)
RETURNS varchar(4000)
AS
BEGIN
DECLARE #Counter as int
DECLARE #strReturnVal varchar(4000)
DECLARE #Len as int
DECLARE #ASCII as int
SET #Counter=0
SET #Len=LEN(#inputString)
SET #strReturnVal = ''
WHILE #Counter<=#Len
BEGIN
SET #Counter = #Counter +1
SET #ascii= ASCII(SUBSTRING(#inputString,#counter,1))
IF(#ascii BETWEEN 65 AND 90) OR (#ascii BETWEEN 97 AND 122)
BEGIN
SET #strReturnVal = #strReturnVal + (SUBSTRING(#inputString,#counter,1))
END
END
RETURN #strReturnVal
END
and
CREATE FUNCTION [fn].[StripToNumeric]
(
#inputString nvarchar(4000)
)
RETURNS Float
AS
BEGIN
DECLARE #Counter as int
DECLARE #strReturnVal varchar(4000)
DECLARE #ReturnVal Float
DECLARE #Len as int
DECLARE #ASCII as int
SET #Counter=0
SET #Len=LEN(#inputString)
SET #strReturnVal = ''
IF #inputString IS NULL
BEGIN
Return NULL
END
-- swap out comma for decimal
SET #inputString = REPLACE(#inputString, ',', '.')
IF #Len = 0 OR LEN(LTRIM(RTRIM(#inputString))) = 0
BEGIN
SET #ReturnVal=0
END
ELSE
BEGIN
WHILE #Counter<=#Len
BEGIN
SET #Counter = #Counter +1
SET #ascii= ASCII(SUBSTRING(#inputString,#counter,1))
IF(#ascii BETWEEN 48 AND 57) OR (#ascii IN (46,37))
BEGIN
SET #strReturnVal = #strReturnVal + (SUBSTRING(#inputString,#counter,1))
END
END
if RIGHT(#strReturnVal,1)='%'
BEGIN
SET #strReturnVal = LEFT(#strReturnVal,len(#strReturnVal)-1)
SET #strReturnVal = CAST((CAST(#strReturnVal AS FLOAT)/100) AS nvarchar(4000))
END
SET #ReturnVal = ISNULL(#strReturnVal,0)
END
RETURN #ReturnVal
END
Notes
This will not affect your current use but the StripToNumeric checks is a percentage sign is present and converts to a decimal so it you pass it 25% it will return 0.25.
This will not work if you use full postcodes such as SK1 1AB as it would sort by SKAB and then 11
It will work on postcodes with shorter prefixes such M34 (That's Denton if I remember correctly ! :) )

Answer 5

You didn't specify database you use; this is an Oracle example. Hopefully, you'll be able to "convert" it to something else.
The idea is: using regular expressions (which seem to be quite handy in such cases), split postcode to two parts: letters and numbers. As REGEXP_SUBSTR returns a string, I applied the TO_NUMBER function to a "numeric" part of the postcode in order to properly sort it.
SQL> with test (postcode) as
2 (select 'sk1' from dual union
3 select 'sk11' from dual union
4 select 'sk13' from dual union
5 select 'sk2' from dual
6 )
7 select postcode
8 from test
9 order by regexp_substr(postcode, '^[[:alpha:]]+'), --> letters
10 to_number(regexp_substr(postcode, '[[:digit:]]+$')); --> numbers
POST
----
sk1
sk2
sk11
sk13
SQL>