Qlikview best pratices the concept of qvd

QlikView QVD’s
A QVD (QlikView Data) file is a file containing a table of data that QlikView has extracted from one or more data sources. QVD is a native QlikView format and can only be written to and read by QlikView.

Creating and loading from QVD Files
QVD files should be created via one QlikView application then the final end user applications should be sourced from these files. The simple diagram below shows this 2 step process.

QVD Load Application

QVD Files Created

Populate End User Application

To create a QVD, the Store function should be used. A simple script example is below. It is also good practice to delete all of the tables created within your load application (using the Drop function) to free memory.
Data: Load ID, Description FROM C:\Data.xls (biff, embedded labels, table is [Core Data$]); Store Data into C:\Data.qvd; Drop Table Data;

In this example, you now have a QVD file on your C drive that can be used as a source for your end user analysis.

Why Use QVD’s?
• • • • Faster data loads Incremental data loads Large data loads Joining QlikView Applications/Data

Faster Data Loads
Loading data in to a QlikView application from a QVD file will be 10-100 times faster than pulling your data direct from the source database. QVD files will be read in two different ways, Fast and Super-Fast. Fast QVD’s – Loading data from a QVD file, when you have then added some calculations/IF statements. Super-Fast QVD’s – If you can build the QVD to hold all of the data you require (therefore when the data is added to your application all you have to do is rename columns and add no calculations, extra columns or joins), the QVD will be read at the optimum speed.

Author: ABY, QlikTech UK.

Incremental Data Loads
In organisations where data volumes are large or batch windows are small, there will be a requirement to implement incremental loads therefore only load data that has changed or added since your last load. These types of data