Optimizing aggregation of tree branch data in SQL Server 2008 (recursion)

Question

I have a table containing the stages and sub-stages of some projects, as well as a table with specific tasks and estimated costs.
I need to somehow combine each level (steps / sub-steps) to find out how much it costs, but do it with minimal cost for performance.

To illustrate this, I will use the following data structure:

CREATE TABLE stage
(
    id int not null,
    fk_parent int
)

CREATE TABLE task
(
    id int not null,
    fk_stage int not null,
    cost decimal(18,2) not null default 0
)

with the following data:

==stage==
id  fk_parent
1   null
2   1
3   1

==task==
id  fk_stage  cost
1   2         100
1   2         200
1   3         600

I want to get a table containing the total costs for each branch. Something like that:

Stage ID      Total Cost
1             900
2             300
3             600

, . , . , . , stage , D , D - (), . , .

SO,

, . 2 stage .

...
calculated_cost decimal(18,2),
date_calculated_cost datetime
...

, , datetime, , ( ). , stage date_calculated_cost, , , calculated_cost.

( stage, )
( )
, , ( , )
.

, , .

Answer 1

1. .

• .
• CTE .
• temp.
• temp.
• temp

. , cteCost, cteLevel.

;with cteCost as
(
  select s.id,
         s.fk_parent,
         isnull(sum(t.cost), 0) as cost
  from stage as s
    left outer join task as t
      on s.id = t.fk_stage
  group by s.id, s.fk_parent
),
cteLevel as
(
  select cc.id,
         cc.fk_parent,
         cc.cost,
         1 as lvl
  from cteCost as cc
  where cc.fk_parent is null
  union all
  select cc.id,
         cc.fk_parent,
         cc.cost,
         lvl+1
  from cteCost as cc
    inner join cteLevel as cl
      on cc.fk_parent = cl.id       
)
select *
into #task
from cteLevel

create clustered index IX_id on #task (id)
create index IX_lvl on #task (lvl, fk_parent)

declare @lvl  int
select @lvl = max(lvl)
from #task

while @lvl > 0
begin

  update T1 set
    T1.cost = T1.cost + T2.cost
  from #task as T1
    inner join (select fk_parent, sum(cost) as cost
                from #task
                where lvl = @lvl
                group by fk_parent) as T2
      on T1.id = T2.fk_parent

  set @lvl = @lvl - 1
end

select id as [Stage ID],
       cost as [Total Cost] 
from #task

drop table #task

2. task, calculated_cost stage.

create trigger tr_task 
on task 
after insert, update, delete
as
  -- Table to hold the updates
  declare @T table
  (
    id int not null, 
    cost decimal(18,2) not null default 0
  )

  -- Get the updates from inserted and deleted tables
  insert into @T (id, cost)
  select fk_stage, sum(cost)
  from (
          select fk_stage, cost
          from inserted
          union all
          select fk_stage, -cost
          from deleted
       ) as T   
  group by fk_stage

  declare @id int
  select @id = min(id)
  from @T

  -- For each updated row
  while @id is not null
  begin

    -- Recursive update of stage
    with cte as 
    (
      select s.id,
             s.fk_parent
      from stage as s
      where id = @id
      union all
      select s.id,
             s.fk_parent
      from stage as s
        inner join cte as c
          on s.id = c.fk_parent    
    )
    update s set
      calculated_cost = s.calculated_cost + t.cost 
    from stage as s
      inner join cte as c
        on s.id = c.id
      cross apply (select cost
                   from @T
                   where id = @id) as t   

    -- Get the next id
    select @id = min(id)
    from @T
    where id > @id
  end