Interview point of view ?? .. Hmm .. well, I would say , Know more about qvd, love it. Then interviewer loves you back.
QVD .. Qlikview data files is a local format / qlikview's local format to save data.
Beauty of QVD is one of the secret sauces of Qlikvew.
We can pull data from any relational or irrelational databases , you must be knowing this.
Using qlikview we can pull data even from Excell sheets and from many data sources.
After pulling data from database using preceding load, we apply transformations etc., to it and we store those as a QVD file.
Then we drop or delete the preceding load and import the QVD file into qlikview.
Since QVD has a great algorithm to compress data , pulling data from it is real fast and reports can be generated dynamically with no lagging.
If there is any lagging , you need to see How Optimized The QVD is .. and also many other things you need to consider.
I just gave you an over view of what QVD is ..
You need to know Binary load, Incremental load, auto incremental load, auto appending the data etc ..
Do some R and D , it will help you for sure.
Have a happy week ahead.
Please read the "Help" on QVD files topics. This will cover all the information you need.
A QVD (QlikView Data) file is a file containing a table of data exported from QlikView. QVD is a native QlikView format and can only be written to and read by QlikView. The file format is optimized for speed when reading data from a QlikView script but it is still very compact. Reading data from a QVD file is typically 10-100 times faster than reading from other data sources.
QVD files can be read in two modes: standard (fast) and optimized (faster). The selected mode is determined automatically by the QlikView script engine. Optimized mode can be utilized only when all loaded fields are read without any transformations (formulas acting upon the fields), though the renaming of fields is allowed. A WHERE clause causing QlikView to unpack the records will also disable the optimized load.
A QVD file holds exactly one data table and consists of three parts:
QVD files can be used for many purposes. At least four major uses can be easily identified. More than one may apply in any given situation:
By buffering non-changing or slowly changing blocks of input data in QVD files, script execution becomes considerably faster for large data sets.
The amount of data fetched from external data sources can also be greatly reduced. This reduces work load on external databases and network traffic. Furthermore, when several QlikView scripts share the same data it is only necessary to load it once from the source database into a QVD file. The other applications can make use of the same data via this QVD file.
With the Binary script statement it is possible to load data from only one single QlikView application into another one, but with QVD files a QlikView script can combine data from any number of QlikView applications. This opens up possibilities e.g. for applications consolidating similar data from different business units etc.
In many common cases the QVD functionality can be used for facilitating incremental load, i.e. exclusively loading new records from a growing database.
To learn more about the use of QVD files and Incremental Load, follow the link below:
A QVD file can be created by one of three different methods:
There is no difference between the resulting QVD files, e.g. with regard to reading speed etc.
A QVD file can be read into or accessed by QlikView by the following methods:
load * from xyz.qvd (qvd);
load Name, RegNo from xyz.qvd (qvd);
load Name as a, RegNo as b from xyz.qvd (qvd);