DROP TABLE IF EXISTS dbo.tbl
GO

CREATE TABLE dbo.tbl (a INT, b INT, c INT, d INT)
GO

DROP TABLE IF EXISTS #t
SELECT [name] = ',' + [name]
INTO #t
FROM sys.columns
WHERE [object_id] = OBJECT_ID('dbo.tbl')

DECLARE @rn INT = @@rowcount

DROP TABLE IF EXISTS #variants

;WITH cte AS
(
    SELECT lvl = @rn, x = (
        SELECT [name]
        FROM #t
        FOR XML PATH(''), TYPE).value('.', 'NVARCHAR(MAX)')

    UNION ALL

    SELECT t1.lvl - 1, REPLACE(t1.x, t2.[name], '')
    FROM cte t1
    CROSS APPLY #t t2
    WHERE t1.lvl > 1
)
SELECT DISTINCT x
INTO #variants
FROM cte

SELECT 'select ' + STUFF(x, 1, 1, '') + ' from dbo.tbl'
FROM #variants