SQL Server 2017

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select Customer, Balance
into #a
from (
values
  (1,     250), 
  (2,     500), 
  (1,     205), 
  (2,     600), 
  (2,     700),
  (3,     300),
  (3,     500),
  (3,     250)
)v(Customer, Balance)
8 rows affected

DECLARE 
    @columns NVARCHAR(MAX) = '',
    @sql     NVARCHAR(MAX) = '';


 SELECT Customer, Balance, Col = ROW_NUMBER() OVER (PARTITION BY Customer ORDER BY [Balance] DESC)
 into #b
 FROM #a
 
SELECT @columns += QUOTENAME(Col) + ','
from (SELECT DISTINCT Col FROM #b) A

-- remove the last comma
SET @columns = LEFT(@columns, LEN(@columns) - 1);


SET @sql = 'SELECT * FROM ( SELECT Customer, Balance, Col FROM  #b) src PIVOT( MAX([Balance]) FOR Col IN ('+ @columns +')) AS pivot_table;';
 
-- execute the dynamic SQL
EXECUTE sp_executesql @sql;


Customer
1
2
3


1
250
205
null

2
700
600
500

3
500
300
250


SELECT STRING_AGG(QUOTENAME(Col), ', ')
from (SELECT DISTINCT Col FROM #b) A


(No column name)


[1], [2], [3]


DECLARE  @columns NVARCHAR(MAX) = ''
SELECT @columns = (
  SELECT QUOTENAME(Col) + ', '
  FROM (SELECT DISTINCT Col FROM #b) A
 
  FOR XML PATH(''), TYPE
                   ).value('.','varchar(max)')
SELECT @columns                  


(No column name)


[1], [2], [3],