Use STUFF function to insert at multiple points in a string?

Question

Is there a way that I can replace a substring in SQL server while remaining 'aware' of what I'm replacing so that I can then re-insert that content?

I am building a string of column names to pivot on, and these column names need to be aggregated on in the query.

For example, I have this list of columns as an nvarchar(max) string:

[A], [B], [C]

And I would like to transform this string to look like this:

sum([A]) [A], sum([B]) [B], sum([C]) [C], 

I have just found the stuff function but I don't know how to achieve what I want yet.

But I get the feeling that I can use it to insert substrings instead of using replacing substrings.

Looking at the stuff function:

STUFF( source_string, start, length, add_string )

How do you insert into multiple locations at once?

My current solution is this:

declare @cols nvarchar(max);
declare @colsAggregate nvarchar(max);
declare @sql nvarchar(max);

select @cols = stuff((
    select distinct ',' + quotename(sCode)
    from EntityList EL
    where EL.bActive = 1 for xml path(''), type).value('.', 'nvarchar(max)'),
1, 1, '');

select @colsAggregate = stuff((
    select distinct ', max(' + quotename(sCode) + ') ' + quotename(sCode)
    from EntityList EL
    where EL.bActive = 1 for xml path(''), type).value('.', 'nvarchar(max)'),
1, 1, '');

Answer 1

You need to get it as rows before you can use STUFF.

DECLARE @rows nvarchar(max) = '[A],[B],[C]';
DECLARE @cols nvarchar(max);

SELECT LTRIM(RTRIM(j.value)) FROM STRING_SPLIT(@rows, ',') j

SET @cols = STUFF((SELECT ', ' + (col) 
                   FROM (SELECT LTRIM(RTRIM(j.value)) col FROM STRING_SPLIT(@rows, ',') j) Foo
            FOR XML PATH(''), TYPE
            ).value('.', 'nvarchar(MAX)') 
           ,1,2,'');

SELECT @cols;

SET @cols = STUFF((SELECT ', ' + ('SUM(' + col + ')') 
                   FROM (SELECT LTRIM(RTRIM(j.value)) col FROM STRING_SPLIT(@rows, ',') j) Foo
            FOR XML PATH(''), TYPE
            ).value('.', 'nvarchar(MAX)') 
           ,1,2,'');

SELECT @cols;

SET @cols = STUFF((SELECT ', ' + ('SUM(' + col + ') ' + col) 
                   FROM (SELECT LTRIM(RTRIM(j.value)) col FROM STRING_SPLIT(@rows, ',') j) Foo
            FOR XML PATH(''), TYPE
            ).value('.', 'nvarchar(MAX)') 
           ,1,2,'');

SELECT @cols;
GO

| (No column name) |
| :--------------- |
| [A]              |
| [B]              |
| [C]              |

| (No column name) |
| :--------------- |
| [A], [B], [C]    |

| (No column name)             |
| :--------------------------- |
| SUM([A]), SUM([B]), SUM([C]) |

| (No column name)                         |
| :--------------------------------------- |
| SUM([A]) [A], SUM([B]) [B], SUM([C]) [C] |

dbfiddle here