FOREACH Recursive SQL Statement
Select all Id's where the parent Id is null (All root entries)
Foreach (Id)
   GenerateControlNum(Id, CurrentCounterValue, CurrentCounterValue)

GenerateControlNum(Id, CurrentCounterValue, ParentCounterValue)
    Set Id's ControlNum to CurrentCounterValue
    Set Id's ParentControlNum to CurrentCounterValue

    Increment CurrentCounterValue

    Select All Id's where ParentId == Id (All my direct children)
    Foreach (ChildId)
        GenerateControlNum(ChildId, CurrentCounterValue, Id's ControlNum);

ID                                      ParentId                                ControlNum  ParentControlNum
8C821027-A6F9-E011-AB48-B499BAE13A62    756F981E-A6F9-E011-AB48-B499BAE13A62    0           NULL
D7DB6033-A6F9-E011-AB48-B499BAE13A62    756F981E-A6F9-E011-AB48-B499BAE13A62    0           NULL
D2E36033-A6F9-E011-AB48-B499BAE13A62    C9E36033-A6F9-E011-AB48-B499BAE13A62    0           NULL
8FE66033-A6F9-E011-AB48-B499BAE13A62    58E66033-A6F9-E011-AB48-B499BAE13A62    0           NULL
37EC6033-A6F9-E011-AB48-B499BAE13A62    2FEC6033-A6F9-E011-AB48-B499BAE13A62    0           NULL
41EC6033-A6F9-E011-AB48-B499BAE13A62    2FEC6033-A6F9-E011-AB48-B499BAE13A62    0           NULL
DDED6033-A6F9-E011-AB48-B499BAE13A62    BCED6033-A6F9-E011-AB48-B499BAE13A62    0           NULL
DC69981E-A6F9-E011-AB48-B499BAE13A62    NULL                                    0           NULL
166A981E-A6F9-E011-AB48-B499BAE13A62    NULL                                    0           NULL
4D6A981E-A6F9-E011-AB48-B499BAE13A62    NULL                                    0           NULL
856A981E-A6F9-E011-AB48-B499BAE13A62    NULL                                    0           NULL
F56A981E-A6F9-E011-AB48-B499BAE13A62    NULL                                    0           NULL
2E6B981E-A6F9-E011-AB48-B499BAE13A62    NULL                                    0           NULL
666B981E-A6F9-E011-AB48-B499BAE13A62    NULL                                    0           NULL
9D6B981E-A6F9-E011-AB48-B499BAE13A62    NULL                                    0           NULL

ID                                      ParentId                                ControlNum  ParentControlNum
8C821027-A6F9-E011-AB48-B499BAE13A62    756F981E-A6F9-E011-AB48-B499BAE13A62    22          21
D7DB6033-A6F9-E011-AB48-B499BAE13A62    756F981E-A6F9-E011-AB48-B499BAE13A62    24          21
D2E36033-A6F9-E011-AB48-B499BAE13A62    C9E36033-A6F9-E011-AB48-B499BAE13A62    58          57
8FE66033-A6F9-E011-AB48-B499BAE13A62    58E66033-A6F9-E011-AB48-B499BAE13A62    69          68
37EC6033-A6F9-E011-AB48-B499BAE13A62    2FEC6033-A6F9-E011-AB48-B499BAE13A62    86          85
41EC6033-A6F9-E011-AB48-B499BAE13A62    2FEC6033-A6F9-E011-AB48-B499BAE13A62    88          85
DDED6033-A6F9-E011-AB48-B499BAE13A62    BCED6033-A6F9-E011-AB48-B499BAE13A62    95          94
DC69981E-A6F9-E011-AB48-B499BAE13A62    NULL                                    0           0
166A981E-A6F9-E011-AB48-B499BAE13A62    NULL                                    1           1
4D6A981E-A6F9-E011-AB48-B499BAE13A62    NULL                                    2           2
856A981E-A6F9-E011-AB48-B499BAE13A62    NULL                                    3           3
F56A981E-A6F9-E011-AB48-B499BAE13A62    NULL                                    4           4
2E6B981E-A6F9-E011-AB48-B499BAE13A62    NULL                                    5           5
666B981E-A6F9-E011-AB48-B499BAE13A62    NULL                                    6           6
9D6B981E-A6F9-E011-AB48-B499BAE13A62    NULL                                    7           7

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;with C as
(
  select ID,
         ParentID,
         ControlNum,
         ParentControlNum,
         row_number() over(order by ParentID, ID) - 1 as rn
  from YourTable
)
update C1
set ControlNum = C1.rn,
    ParentControlNum = case when C1.ParentID is null
                         then C1.rn
                         else C2.rn
                       end
from C as C1
  left outer join C as C2
    on C1.ParentID = C2.ID

;with R as
(
  select ID,
         ParentID,
         cast(ID as varchar(max)) as Sort
  from YourTable
  where ParentID is null
  union all
  select T.ID,
         T.ParentID,
         R.Sort+cast(T.ID as varchar(max))
  from YourTable as T
    inner join R
      on R.ID = T.ParentID
),
C as
(
  select ID,
         ParentID,
         row_number() over(order by Sort) - 1 as rn
  from R
)
update T
set ControlNum = C1.rn,
    ParentControlNum = case when C1.ParentID is null
                         then C1.rn
                         else C2.rn
                       end
from YourTable as T
  inner join C as C1
    on T.ID = C1.ID
  left outer join C as C2
    on T.ParentID = C2.ID