string permutations

DECLARE @a nvarchar(100) = 'abbccc';

    WITH a AS(SELECT 1 n UNION ALL SELECT n+1 FROM a WHERE n<len(@a))
    ,b AS
    (
       SELECT CAST('' AS nvarchar(100)) s, CAST(@a AS nvarchar(100)) r, n p
       FROM a
       UNION ALL
       SELECT
          CAST(s+SUBSTRING(r,p,1) AS nvarchar(100)),
          CAST(SUBSTRING(r,1,p-1)+SUBSTRING(r,p+1,999) AS nvarchar(100)),
          n
       FROM a,b
       WHERE p<=len(r)
    )
    SELECT DISTINCT s
    FROM b
    WHERE len(s) = len(@a)
    ORDER BY s
    OPTION (maxrecursion 10000)