QVD Files In QlikView Application

Introduction

QVD is a file with the extension (.qvd). It stores the data of a single table; that means that each row shares the same column name. It is typically created in a load script of a QVD file. The structure of a QVD file is essentially XML format. QVD files of QlikView store data. QVD files are used to provide a logical data solution in a QlikView solution. In some cases QVD files avoid the use of a data warehouse.

QVD files hold only one single table data and also consists of the following three parts:

1. The QVD files consist of well a formed XML header. The XML header describes the available fields in the table and also contains the layout of the information.
    
2. Symbol tables in byte stuffed format.
    
3. Actual table in bit stuffed format.

The QVD files can be read in two modes.

• Standard
   
• Optimized

Standard mode

The standard mode is determined automatically by the QlikView script engine.

Optimized mode

The optimized mode is determined by only when all loaded files are read without any transformation.

Purpose of QVD files

There are the following basic purposes of QVD files.

1. The main purpose of a QVD file is to increas load speed. By unchanging and slowly changing blocks of input data in QVD files, the script execution becomes much faster for large data sets.
    
2. The second purpose of QVD files is incremental load. In this QVD files loads new data from a growing database.
    
3. The third and main purpose of QVD file is decreasing load on the database server, that means that when a huge amount of data is import from an external data source then there is a heavy load generated on the data base server. So by using QVD files we decrease the load on the database server.
    
4. By using QVD files the QlikView script can combine data from any number of QlikView applications. QVD files consolidate data from different and multiple QlikView applications.

Creation of QVD

QVD files are created during the execution of a QlikView load script. QVD file syntax uses a STORE statement because store statements writes current contents of a single table in the data model to a file. It is stored in disk.

Syntax of QVD file

The following is the syntax to create a QVD file.

STORE TableName INTO ..\Data\FileName.qvd (QVD);

Use of QVD files

The following are the multile uses of QVD files.

1. With the use of QVD files, the incremental load can be adopted.
    
2. From data presentation, complex data can be extract.
    
3. With the use of QVD files, parallel data can be extract.
    
4. Unit testing will be easy in heavy load process.
    
5. Data sharing also be happen in data presentation.

How to use QVD files in QlikView application

TableName:
LOAD
FieldList
FROM ..\Data\FileName.qvd (qvd);

Summary

This article introduced QlikView files and also described the syntax and use of QVD files in a QlikView application.