Mapping Load & ApplyMap

[Embers_P_21]

Hello,

I'm going through a QV Essentials book, now on a chapter on Mapping tables.

I'm struggling to get my head around how Category_Map is loaded from a text file and then used within another Mapping table without a matching key (lookup value) which in the case of Category_Map would be ProductCategoryID, while SubCategory_CategoryMap wants to retrieve CategoryName using  ProductSubcategoryID as a lookup value that doesn't exist in the Category_Map table? The Product table where the mapping tables are applied only contains ProductSubcategoryID.

Any clarification on this would be much appreciated, thanks a lot!

ProductCategory text file:

ProductCategoryID CategoryName
1 Bikes
2 Components
3 Clothing
4 Accessories

Sample from ProductSubCategory file:

ProductSubcategoryID	ProductCategoryID	SubCategoryName
1	1	Mountain Bikes
2	1	Road Bikes
3	1	Touring Bikes
4	2	Handlebars
5	2	Bottom Brackets
6	2	Brakes
7	2	Chains

Mapping tables:

//***** Product Category Map ****//

Category_Map:

Directory;

Mapping LOAD 

ProductCategoryID as CategoryID, 

     CategoryName as CategoryName

FROM

QlikViewEssentials\Data\ProductCategory.txt

(txt, codepage is 28591, embedded labels, delimiter is '\t', msq);

// *** SubCategory Name Map ****//

SubCategory_Map:

Mapping LOAD 

    ProductSubcategoryID,

    SubCategoryName;

SQL SELECT *

FROM ProductSubcategory;

// *** SubCategory Category Desc Map *** //

SubCategory_CategoryMap:

Mapping load

ProductSubcategoryID,

ApplyMap('Category_Map', ProductSubcategoryID, 'No Category'); //???????????????????????????????????????//

SQL SELECT *

FROM ProductSubcategory;

Maps applied:

Product:

LOAD ProductID,
ProductLine,
ProductName,
ProductNumber,
ProductSubcategoryID,
ReorderPoint,
SafetyStockLevel,
StandardCost,
Style,
UnitPrice as ListPrice,

if (ProductLine = 'M', 'Mountain',
if (ProductLine = 'R', 'Road',
if (ProductLine = 'S', 'Accessory', 'Components')) ) as ProductLineDesc,

ApplyMap ('SubCategory_Map', ProductSubcategoryID, 'No SubCategory') as [SubCategory Desc],
ApplyMap('SubCategory_CategoryMap', ProductSubcategoryID, 'No Category') as [Category Desc]
;
SQL SELECT *
FROM Product;

[Embers_P_21]

Attaching source files

[Vinod]

Hi, Request you to share the source file which is used in the QlikView Essentials book.