Inventory by LocationId (were locations are hierarchical)

Question

Hi,
I have a problem with an inventory system I'm designing.  It is an inventory system by LocationId.   The problem I have is that the locations are hierarchical.   By hierarchical I mean that a given location might belong to a next location.
For example given the following (simplified) schema of 3 tables (Locations, Articles and Inventory)
CREATE  TABLE Locations (
LocationId                 INTEGER NOT NULL,
ParentLocationId           INTEGER NULL,
CONSTRAINT w_Ub_LLAVE PRIMARY KEY (LocationId)
GO
INSERT INTO Locations (LocationId,ParentLocationId) VALUES (1,NULL);
INSERT INTO Locations (LocationId,ParentLocationId) VALUES (2,NULL);
INSERT INTO Locations (LocationId,ParentLocationId) VALUES (3,NULL);
INSERT INTO Locations (LocationId,ParentLocationId) VALUES (4,1);
INSERT INTO Locations (LocationId,ParentLocationId) VALUES (5,4);
INSERT INTO Locations (LocationId,ParentLocationId) VALUES (6,4);
INSERT INTO Locations (LocationId,ParentLocationId) VALUES (7,5);
CREATE TABLE Articles  (
ItemId                     INTEGER NOT NULL,
Description                VARCHAR(50),
CONSTRAINT ArticlePK PRIMARY KEY (ItemId)
GO
INSERT INTO Articles (ItemId,Description)  VALUES (100,'BREAD');
CREATE TABLE Inventory (
LocationId                 INTEGER NOT NULL,
ItemId                     INTEGER NOT NULL,
Qty                        DECIMAL(14,4) NULL,
CONSTRAINT InventoryPK PRIMARY KEY (LocationId,ItemId)
GO
INSERT INTO Inventory (LocationId,ItemId,Qty) VALUES (1,100,5);
INSERT INTO Inventory (LocationId,ItemId,Qty) VALUES (2,100,5);
INSERT INTO Inventory (LocationId,ItemId,Qty) VALUES (3,100,5);
INSERT INTO Inventory (LocationId,ItemId,Qty) VALUES (4,100,5);
INSERT INTO Inventory (LocationId,ItemId,Qty) VALUES (5,100,5);
INSERT INTO Inventory (LocationId,ItemId,Qty) VALUES (6,100,5);
INSERT INTO Inventory (LocationId,ItemId,Qty) VALUES (7,100,5);
I would like to list the contents by locationId.
For example, if I list LocationId=1 I should get 
5 (in LocationId = 1) + 
5 (in LocationId = 4 which belongs to 1) + 
5 (in LocationId=5 which belongs to 4 which belongs to 1) + 
5 (in LocationId=6 which belongs to 4 which belongs to 1) +
5 (in LocationId=7 which belongs to 5 which belongs to 4 which belongs to 1)
= 25
If I list LocationId=7 I would only get 5 (those in locationId=7)
If I list LocationId=5 I would bet 10 (those in LocationId=5 and those in LocationId=7).
Hopefully I was able to explain myself.   Does anybody know how this could be done?
Thanks,
Edgard

Answer 1

One way to solve this is expanding the hierarchy starting from the node in question all the way down till the last descendant. Then you can join the result to the inventory table to aggregate.
DECLARE @LocationId int =5;
WITH TC AS (
SELECT
LocationId AS ReportsTo,
LocationId
FROM
Locations
WHERE
LocationId = @LocationId
UNION ALL
SELECT
P.ReportsTo,
C.LocationId
FROM
TC AS P
INNER JOIN
Locations AS C
ON C.ParentLocationId = P.LocationId
SELECT
A.ReportsTo,
B.ItemId,
SUM(B.Qty) AS sum_Qty
FROM
TC AS A
INNER JOIN
Inventory AS B
ON A.LocationId = B.LocationId
GROUP BY
A.ReportsTo,
B.ItemId
GO
It gets a little bit more complicated if you want to see all locations, their quantities and the aggregation of the descendants.
WITH TC AS (
SELECT
LocationId AS ReportsTo,
LocationId
FROM
Locations
UNION ALL
SELECT
P.ReportsTo,
C.LocationId
FROM
TC AS P
INNER JOIN
Locations AS C
ON C.ParentLocationId = P.LocationId
, Agg AS (
SELECT
A.ReportsTo,
B.ItemId,
SUM(CASE WHEN A.ReportsTo = B.LocationId THEN B.Qty END) AS Qty,
SUM(B.Qty) AS TotalQty
FROM
TC AS A
INNER JOIN
Inventory AS B
ON A.LocationId = B.LocationId
GROUP BY
A.ReportsTo,
B.ItemId
, LocHie AS (
SELECT
LocationId,
CAST(LocationId AS varbinary(900)) AS SortBy,
0 AS lvl
FROM
Locations
WHERE
ParentLocationId IS NULL
UNION ALL
SELECT
C.LocationId,
CAST(P.SortBy + CAST(ROW_NUMBER() OVER(PARTITION BY P.LocationId ORDER BY C.LocationId) AS binary(8)) AS varbinary(900)),
P.lvl + 1
FROM
LocHie AS P
INNER JOIN
Locations AS C
ON C.ParentLocationId = P.LocationId
SELECT
REPLICATE('|', 8 * lvl) + LTRIM(A.LocationId) AS LocId,
B.ItemID,
B.Qty,
B.TotalQty
FROM
LocHie AS A
LEFT OUTER JOIN
Agg AS B
ON A.LocationId = B.ReportsTo
ORDER BY
A.SortBy;
GO
This approach will not perform well if you have too many levels in the hierarchy and a procedural approach that traverses each level at a time, starting from the leaves, will perform better.
Itzik Ben-Gan has a whole chapter dedicated to Graph theory in his book "Inside Microsoft® SQL Server® 2008: T-SQL Querying".
http://shop.oreilly.com/product/9780735626034.do
AMB
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