SQL Server 2019

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create table Documents(DocumentID int, Filename varchar(50));
create table VariableValues(VariableID int,DocumentID int, ValueCache varchar(50),	ConfigurationID int);
create table Configuration(ConfigurationID int, ConfigName varchar(50));
insert into Documents values(1,'file1.txt');
insert into VariableValues values 
(55,1,'Val1',1),
(56,1,'Val2',1),
(172,1,'Val3',1),
(55,1,'Val1',2),
(56,1,'Val2',2),
(172,1,'Val3',2);
insert into Configuration values
(1,'Default'),
(2,'First');
9 rows affected

select Filename, Val1 as att1,	Val2 as att2, Val3 as att3, ConfigName  from
(
select Documents.Filename, VariableValues.ValueCache,Configuration.ConfigName
from 
Documents inner join VariableValues
on Documents.DocumentID=VariableValues.DocumentID
inner join Configuration
on Configuration.ConfigurationID = VariableValues.ConfigurationID
 ) D
PIVOT
  (MAX(ValueCache) for ValueCache in (Val1,	Val2, Val3)) P


Filename
att1
att2
att3
ConfigName


file1.txt
Val1
Val2
Val3
Default

file1.txt
Val1
Val2
Val3
First


DECLARE @valCols AS NVARCHAR(MAX), @sqlQr  AS NVARCHAR(MAX)

select @valCols = STUFF((SELECT distinct ',' + QUOTENAME(ValueCache) 
                    from VariableValues FOR XML PATH(''), TYPE).value('.', 'NVARCHAR(MAX)') 
        ,1,1,'')

set @sqlQr = 'SELECT Filename, ' + @valCols + ', ConfigName from 
(
select Documents.Filename, VariableValues.ValueCache,Configuration.ConfigName
from 
Documents inner join VariableValues
on Documents.DocumentID=VariableValues.DocumentID
inner join Configuration
on Configuration.ConfigurationID = VariableValues.ConfigurationID
 ) D
 PIVOT
(MAX(ValueCache) for ValueCache in ('+ @valCols+ ')) P'
execute(@sqlQr)


Filename
Val1
Val2
Val3
ConfigName


file1.txt
Val1
Val2
Val3
Default

file1.txt
Val1
Val2
Val3
First