declare @input nvarchar(100) = 'abbccc';
   
with nums as
(
   select n = 1           -- base case starting at 1
   
   union all
   
   select n = n+1         -- recursive case:  next number = 2, 3, ... len(@input)
   from nums
   where n < len(@input)  -- stop and don't run if n equal the len(@input)
)
,perms as
(
   select                                      -- base case for recursion
      string = cast(''     as nvarchar(100)),  -- string we are generating, start as empty string
      remain = cast(@input as nvarchar(100)),  -- remaining characters to append to our string
      pos    = n                               -- position of next character in remaining string to append to base case
   from nums
   
   union all
   
   -- recursive case where we append 1 character per step
   select
      -- append character at position pos to base string
      string = cast(string + substring(remain,pos,1) as nvarchar(100)),
      -- remove character we added from remaining characters
      remain = cast(stuff(remain,pos,1,'') as nvarchar(100)),
      -- all possible positions of remaining characters
      pos    = nums.n
   from perms, nums
   -- only look at possible valid positions
   -- this forces the recursion to terminate when remain is empty
   where pos <= len(remain)
)
select distinct string
from perms
where len(string) = len(@input)
order by string
option (maxrecursion 10000)