Optimize for speed a simple stored procedure - sql

Question

In SQL 2008 I've this easy-but-bad-write sp that works:
ALTER PROCEDURE [dbo].[paActualizaCapacidadesDeZonas]
AS
BEGIN
SET NOCOUNT ON;
DECLARE #IdArticulo AS INT
DECLARE #ZonaAct AS INT
DECLARE #Suma AS INT
UPDATE CapacidadesZonas SET Ocupado=0
DECLARE csrSumas CURSOR FOR
SELECT AT.IdArticulo, T.NumZona, SUM(AT.Cantidad)
FROM ArticulosTickets AT
INNER JOIN Tickets T ON AT.IdTicket = T.IdTicket
GROUP BY AT.IdArticulo, T.NumZona
OPEN csrSumas
FETCH NEXT FROM csrSumas INTO #IdArticulo, #ZonaAct, #Suma
WHILE ##FETCH_STATUS = 0
BEGIN
UPDATE CapacidadesZonas SET Ocupado = #Suma
WHERE NumZona = #ZonaAct AND IdArticulo = #IdArticulo
FETCH NEXT FROM csrSumas INTO #IdArticulo, #ZonaAct, #Suma
END
CLOSE csrSumas
DEALLOCATE csrSumas
END
I know: I must avoid cursors, so I'm pretty sure that it can be done in a much proper way.
I've tried with a single Update query:
UPDATE CapacidadesZonas SET Ocupado =
(SELECT SUM(AT.Cantidad)
FROM ArticulosTickets AT
INNER JOIN Tickets T ON AT.IdTicket = T.IdTicket
GROUP BY AT.IdArticulo, T.NumZona)
But this is really wrong, because the select returns more than one row.
I'm feeling bad with this, because it is supposed must be easy for me, but I can't find the equivalent query.
Any suggestions?
Thanks in advance.

Answer 1

There are many different solutions to this problem-- see this article for a few options. Here's one way: use a derived table.
UPDATE CapacidadesZonas SET Ocupado=0 WHERE Ocupado <> 0;
UPDATE CapacidadesZonas
SET Ocupado = SUM(s.Cantidad)
FROM CapacidadesZonas C INNER JOIN
(
SELECT T.NumZona, AT.IdArticulo, SUM(AT.Cantidad) as Ocupado
FROM ArticulosTickets AT
INNER JOIN Tickets T ON AT.IdTicket = T.IdTicket
GROUP BY AT.IdArticulo, T.NumZona
) s ON s.NumZona = C.NumZona AND s.IdArticulo = C.IdArticulo;
Caveats:
are you expecting that the CapacidadesZonas table is available to a live application while the update is happening? If so you may have a locking or perf issue since SQL will may lock the whole table for the update of every row. If this is the case, consider doing your update in batches (e.g. of 1,000 rows each). UPDATE TOP makes batching easy.
sometimes SQL picks a suboptimal plan for queries like this. it may be faster to load a temp table (like in astander's solution above, but using a temp table instead of a table var) than to try to do the update as a single query. If you do this, remember to make sure there's an index on (IDArticulo, NumZona) on the the temp table before you do your update.

Answer 2

Try:
UPDATE cz
SET Ocupado = SUM(AT.Cantidad)
FROM CapacidadesZonas as cz
INNER JOIN ArticulosTickets AT ON cz.numZona = at.numZona and cz.IDArticulo = at.IDArticulo
INNER JOIN Tickets T ON AT.IdTicket = T.IdTicket
GROUP BY AT.IdArticulo, T.NumZona