Si no se sabe cuántos niveles hay en la jerarquía?
Entonces, tal desafío a menudo se realiza a través de un CTE recursivo.
Fragmento de ejemplo:
--
-- Using table variables for testing reasons
--
declare @customertest table (cid int primary key, upid int);
declare @conftest table (cid int, confname varchar(6) default 'budget', confvalue int);
--
-- Sample data
--
insert into @customertest (cid, upid) values
(1,0), (2,1), (3,1), (4,2), (5,2), (6,3),
(7,5), (8,5), (9,8), (10,9);
insert into @conftest (cid, confvalue) values
(1,1000), (2,700), (3,300), (4,100), (5,200), (6,300);
-- The customer that has his own budget, or not.
declare @customerID int = 10;
;with RCTE AS
(
--
-- the recursive CTE starts from here. The seed records, as one could call it.
--
select cup.cid as orig_cid, 0 as lvl, cup.cid, cup.upid, budget.confvalue
from @customertest as cup
left join @conftest budget on (budget.cid = cup.cid and budget.confname = 'budget')
where cup.cid = @customerID -- This is where we limit on the customer
union all
--
-- This is where the Recursive CTE loops till it finds nothing new
--
select RCTE.orig_cid, RCTE.lvl+1, cup.cid, cup.upid, budget.confvalue
from RCTE
join @customertest as cup on (cup.cid = RCTE.upid)
outer apply (select b.confvalue from @conftest b where b.cid = cup.cid and b.confname = 'budget') as budget
where RCTE.confvalue is null -- Loop till a budget is found
)
select
orig_cid as cid,
confvalue
from RCTE
where confvalue is not null;
Resultado:
cid confvalue
--- ---------
10 200
Por cierto, el CTE recursivo usa la APLICACIÓN EXTERNA porque MS SQL Server no permite que se use una UNIÓN EXTERNA IZQUIERDA allí.
¿Y si es seguro que hay un máximo de 1 nivel de profundidad para el upid con un presupuesto?
Entonces bastaría con uniones izquierdas simples y una fusión.
Por ejemplo:
select cup.cid, coalesce(cBudget.confvalue, upBudget.confvalue) as confvalue
from @customertest as cup
left join @conftest cBudget on (cBudget.cid = cup.cid and cBudget.confname = 'budget')
left join @conftest upBudget on (upBudget.cid = cup.upid and upBudget.confname = 'budget')
where cup.cid = 8;
