订单串联字段

Question

I have a field which is a concatenation of single letters. I am trying to order these strings within a view. These values can't be hard coded as there are too many. Is someone able to provide some guidance on the function to use to achieve the desired output below? I am using MSSQL.

Current output

CustID | Code
123    | BCA

Desired output

CustID | Code
123    | ABC

I have tried using a UDF

CREATE FUNCTION [dbo].[Alphaorder] (@str VARCHAR(50))
returns VARCHAR(50)
  BEGIN
      DECLARE @len    INT,
              @cnt    INT =1,
              @str1   VARCHAR(50)='',
              @output VARCHAR(50)=''

      SELECT @len = Len(@str)
      WHILE @cnt <= @len
        BEGIN
            SELECT @str1 += Substring(@str, @cnt, 1) + ','

            SET @cnt+=1
        END

      SELECT @str1 = LEFT(@str1, Len(@str1) - 1)

      SELECT @output += Sp_data
      FROM  (SELECT Split.a.value('.', 'VARCHAR(100)') Sp_data
             FROM   (SELECT Cast ('<M>' + Replace(@str1, ',', '</M><M>') + '</M>' AS XML) AS Data) AS A
                    CROSS APPLY Data.nodes ('/M') AS Split(a)) A
      ORDER  BY Sp_data

      RETURN @output
  END

This works when calling one field ie.

Select CustID, dbo.alphaorder(Code)
from dbo.source
where custid = 123

however when i try to apply this to top(10) i receive the error "Invalid length parameter passed to the LEFT or SUBSTRING function."

Keeping in mind my source has ~4million records, is this still the best solution?

Unfortunately i am not able to normalize the data into a separate table with records for each Code.

Answer 1

This doesn't rely on a id column to join with itself, performance is almost as fast as the answer by @Shnugo:

SELECT
  CustID, 
  (
    SELECT
      chr
    FROM
      (SELECT TOP(LEN(Code)) 
         SUBSTRING(Code,ROW_NUMBER() OVER(ORDER BY (SELECT NULL)),1)
       FROM sys.messages) A(Chr)
       ORDER by chr
       FOR XML PATH(''), type).value('.', 'varchar(max)'
      ) As CODE
FROM
  source t

Answer 2

First of all: Avoid loops...

You can try this:

DECLARE @tbl TABLE(ID INT IDENTITY, YourString VARCHAR(100));
INSERT INTO @tbl VALUES ('ABC')
                       ,('JSKEzXO')
                       ,('QKEvYUJMKRC');

--the cte will create a list of all your strings separated in single characters.
--You can check the output with a simple SELECT * FROM SeparatedCharacters instead of the actual SELECT

WITH SeparatedCharacters AS
(
    SELECT *
    FROM @tbl
    CROSS APPLY
    (SELECT TOP(LEN(YourString)) ROW_NUMBER() OVER(ORDER BY (SELECT NULL)) FROM master..spt_values) A(Nmbr)
    CROSS APPLY
    (SELECT SUBSTRING(YourString,Nmbr,1))B(Chr)
)
SELECT ID,YourString
      ,(
        SELECT Chr As [*]
        FROM SeparatedCharacters sc1
        WHERE sc1.ID=t.ID
        ORDER BY sc1.Chr
        FOR XML PATH(''),TYPE
       ).value('.','nvarchar(max)') AS Sorted
FROM @tbl t;

The result

ID  YourString  Sorted
1   ABC         ABC
2   JSKEzXO     EJKOSXz
3   QKEvYUJMKRC CEJKKMQRUvY

The idea in short

The trick is the first CROSS APPLY . This will create a tally on-the-fly . You will get a resultset with numbers from 1 to n where n is the length of the current string.

The second apply uses this number to get each character one-by-one using SUBSTRING() .

The outer SELECT calls from the orginal table, which means one-row-per-ID and use a correalted sub-query to fetch all related characters. They will be sorted and re-concatenated using FOR XML . You might add DISTINCT in order to avoid repeating characters.

That's it :-)

Hint: SQL-Server 2017+

With version v2017 there's the new function STRING_AGG() . This would make the re-concatenation very easy:

WITH SeparatedCharacters AS
(
    SELECT *
    FROM @tbl
    CROSS APPLY
    (SELECT TOP(LEN(YourString)) ROW_NUMBER() OVER(ORDER BY (SELECT NULL)) FROM master..spt_values) A(Nmbr)
    CROSS APPLY
    (SELECT SUBSTRING(YourString,Nmbr,1))B(Chr)
)
SELECT ID,YourString
      ,STRING_AGG(sc.Chr,'') WITHIN GROUP(ORDER BY sc.Chr) AS Sorted
FROM SeparatedCharacters sc
GROUP BY ID,YourString;

Answer 3

Considering your table having good amount of rows (~4 Million), I would suggest you to create a persisted calculated field in the table, to store these values. As calculating these values at run time in a view, will lead to performance problems.

If you are not able to normalize, add this as a denormalized column to the existing table.

I think the error you are getting could be due to empty codes.

If LEN(@str)  = 0
BEGIN
  SET @output = ''
END
ELSE
BEGIN
... EXISTING CODE BLOCK ...
END

Answer 4

I can suggest to split string into its characters using referred SQL function. Then you can concatenate string back, this time ordered alphabetically.

Are you using SQL Server 2017? Because with SQL Server 2017, you can use SQL String_Agg string aggregation function to concatenate characters splitted in an ordered way as follows

select 
    t.CustId, string_agg(strval, '') within GROUP (order by strval) 
from CharacterTable t
cross apply dbo.SPLIT(t.code) s
where strval is not null 
group by CustId
order by CustId 

If you are not working on SQL2017, then you can follow below structure using SQL XML PATH for concatenation in SQL

select 
    CustId, 
    STUFF(
    (
    SELECT
      '' + strval
    from CharacterTable ct
    cross apply dbo.SPLIT(t.code) s
    where strval is not null 
    and t.CustId = ct.CustId
    order by strval
    FOR XML PATH('')
    ), 1, 0, ''
  ) As concatenated_string
from CharacterTable t
order by CustId