Top most important Qlikview interview questions and answers by Experts:

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1)Optimized and unoptimized QVD Load Situations?

Loading the data without performing any transformations is unoptimized load. Loading the data with some transformations is Optimized load. Ex : Load * from tab1 where Year = 2014;

2) Explain 3 tier architecture implementation while deploying QlikView application?

In First Tier: Data is loaded from the Database and stored in QVDs.

In Second Tier: Data is loaded from QVDs and tranform the data based on business needs.

In Third Tier: Using the Binary load the Qlikview file created in Tier II is loaded in to the Qlikview file and all chart objects are created in this Tier.

3) Briefly explain how does QlikView storage the data internally?

data is binary format

4)What are the restrictions of Binary Load?

Binary load should be used only once in qvw application and it should be the first line in script editor page.

5) How are NULLS implemented in QlikView?

The way in which QlikView’s associative engine works means Nulls don’t really exist in the data it holds, a Null is simply an absence of a data item.For example if a field value is missing we cant make selection on empty list box. We can replace these null values with our required values(NA,0, etc) .

6) How do you optimize QlikView Application? (What tools are used and where do you start?

For Optimization we can optimized the QVD which is used in the QVW files in the backend. For QVW optimization i believe not use any tools we can manually remove unwanted fields form data model or comment it, remove most complex logics from the load script or create it with the simple way because it will take long time for loading. If using large data base file try to create the incremental load for the QVD or load latest data only.

7) What is the difference between Subset ratio & Information Density?

Information Density: is the number of records that have values (i.e. not NULL) in this field as compared to the total number of records in the table.

SubSet Ratio:Subset ratio, which shows the percentage of all distinct values for a field in the table compared to all the distinct values for that field in the entire data model.

8) What is the difference between ODBC, OLE DB & JDBC?

JDBC is Java Data Base Connectivity .
ODBC is Open Data Base Connectivity .
Differences :
ODBC is from Microsoft .
JDBC is standard java interface to communicate with a database.
Both are used to connect with the database.
ODBC can’t be directly used with Java because it uses a C interface.
ODBC makes use of pointers which have been removed totally from java.
ODBC mixes simple and advanced features together and has complex options for simple queries.But JDBC is simple which allows advanced capabilities when required.

JDBC drivers are written in java and JDBC code is automatically installable, secure, and portable on all platforms.

JDBC API is a Java Interface and is built on ODBC.
JDBC retains some of the basic feature of ODBC.

9) What is the use of Crosstable prefix in QlikView Load Script?

Incremental load is a very common task in relation to data bases. It is defined as loading nothing but new or changed records from the database. All other data should already be available, in one way or another. With QVD Files it is possible to perform incremental load in most cases. The basic process is described below:

Load the new data from Database table (a slow process, but loading a limited number of records).

Load the old data from QVD file (loading many records, but a much faster process).

Create a new QVD file.

Repeat the procedure for every table loaded.

The following basic cases can be identified:

1) Case 1: Append Only (typically log files)

2) Case 2: Insert Only (No Update or Delete)

3) Case 3: Insert and Update (No Delete)

4) Case 4: Insert, Update and Delete

10) What is Mapping Load & ApplyMap() ?

Mapping Load: The mapping prefix is used on a load or select statement to create a mapping table, these tables are different from other tables. They will be stored in separate area of memory and used as mapping tables during script execution. After execution they will automatically drop.

Ex. Mapping (Load Statement/Select Statement)

Apply Map: used for mapping data from one source to another at load time.

Ex. Applymap(Mapname, expr,[default expr])

11) Synthetic Keys in QlikView and how & when to avoid them?

In two or more tables more than one common field is there synthetics keys will be formed: we can remove in the following ways 1.commenting 2.rename 3.join 4.Qulify 5.linktable 6.concatenation

12) Explain QlikView Resident Load?

Resident Load:- It’s a part of loading data into qlikview application.
It means, loading data (one or more fields) from a table (which is already loaded into qlikview application).

Syntax:- Load
Field_1
Field_2
…
Resident <Table_Name>;

13) What is initial load and incremental load?

Initial load means, when ever the target table is empty on that time we load from starting year data to up to this day data we are loading into the target like facts or dataware house or datamarts.This is initial loading.

Incremental loading means just coming data that means today data that data load into target table this is called as incremental loading(already previous data is loading into targets then just now coming data is loading into target table that means updated data)it takes loading time is 3 to 4 hours.

Another difference that the initial load jobs were set to first truncate the tables and then do a complete load and the incremental load was set to insert new rows and update existing rows for DIMENSION Tables. Facts jobs were same (truncate and complete load).

14) What is Incremental Load in qlikview?

Load the new data from Database table (a slow process, but loading a limited number of records).

Load the old data from QVD file (loading many records, but a much faster process).

Create a new QVD file.

Repeat the procedure for every table loaded.

The following basic cases can be identified:

1) Case 1: Append Only (typically log files)

2) Case 2: Insert Only (No Update or Delete)

3) Case 3: Insert and Update (No Delete)

4) Case 4: Insert, Update and Delete

15) Explain Aggr Function?

Think of the aggr() function as making a temporary table. For instance, let’s say we have this real table of data:

Customer, Value
A, 20
A, 30
B, 10
B, 15
C, 40

Now, as a nonsense requirement, let’s say that we’re looking for maximum value by customer, and then the minimum of THAT value across customers. Our max value by customer is A=30, B=15, C=40. Our min of those is 15. Note how we built a temporary table with three rows while calculating it. Aggr() is one way to build this temporary table. Our dimension is Customer, and our expression is max(Value). We could build this as a real chart, but instead we want to use it in an expression without doing so. The general format for aggr() is this:

aggr(expression, dimensions)

So in our case:

aggr(max(Value),Customer)

We’re trying to extract the minimum from that temporary table, that list of values, so we just enclose it in min():

min(aggr(max(Value),Customer))

16) What is the use of FirstSortValue in QlikView?

SET or a LET statement is often used To define the variable. The SET statement is used when you want a variable to hold the string or numeric value that is to the right of the Equal (=) sign.

The LET statement is used when you need to evaluate what is to the right of the Equal sign

e.g

set myVar=52 the result is 52″

Let myVar=5*2 the result is 10″

17) Explain Qlikview architecture?

QlikView deployments have three main infrastructure components:

1.QlikView Developer : Is a Windows-based desktop tool that is used by designers and developers to create

1) a data extract and transformation model and

2) to create the graphical user interface (or presentation layer).

2.QlikView Server (QVS) : Handles the communication between clients and the QlikView applications. It loads QlikView applications into memory and calculates and presents user selections in real time.

3.QlikView Publisher: Loads data from different data sources (oledb/odbc, xml, xls), reduces the QlikView application and distributes to a QVS.

Because QlikView Server and Publisher have different roles and handle CPU and memory differently it’s considered a best practice to separate these two components on different servers.

18) Set analysis in qlikview ?

Used for set of groups .. mostly used in arrgeted function like sum (year) used sales of current year VS last year.

19) What is Synthetic key and how to avoid it in QlikView?

It is undesirable to have multiple common keys across multiple tables in a QlikView data structure. This may cause QlikView to use complex keys (a.k.a. synthetic keys) to generate the connections in the data structure. Synthetic keys are generally resource heavy and may slow down calculations and, in extreme cases, overload anapplication. They also make a document harder to understand and maintain. Thereare some cases where synthetic keys cannot be avoided (e.g. Interval Match tables),but, in general, synthetic keys should always be eliminated, if possible.

comment the fileds in load script
rename the fileds in load script
rename the fileds using UNQUALIFY operator;
20) Difference between keep and joins ?

Left Keep and Left join gives the same output. The only difference is that Left Keep keeps the Table separate in Data Model, whereas Left join merges the Tables that are joined.

21) Difference between Straight table and pivot table ?

Pivot Table –

1) A pivot table is better at grouping: you can easily see which group a specific row belongs to, and a group can have a subtotal.

2) You can also display a pivot table like a cross table (one or several horizontal dimensions).

3) But when you sort a pivot table, you have to sort it first according to the first dimension, then according to the next, etc.

You cannot sort it any way you want.

Straight Table-

A straight table is better at sorting than a pivot table: you can sort it according to any column.

But it is not so good at grouping. Subtotals are not possible, for instance.

22) Which graph will you used for two years difference sale ?

BAR Graph

23) What is Incremental Load in qlikview?

As BI apps are expected to deal with larger and larger amounts of data the amount of time that it takes to retrieve that data becomes a serious issue. This could be due to shear volume of data or the need for frequent refreshes. Either way, you do not want to be pulling all of the data all of the time. What you want to be able to do is just pull the data that has changed, append to that the data that you stored away previously and then get back to the business of analyzing. This will reduce load on the source database, the network infrastructure and your QlikView server.

24) Whta is Inline memory in QlikView ?

Create table or add field to table .

25) what is Set and let in QlikView and difference between it?

SET or a LET statement is often usedTo define the variable. The SET statement is used when you want a variableto hold the string or numeric value that is to the right of the Equal (=) sign.

The LET statement is used when you need to evaluate what is to the right of the Equal sign

e.g

set myVar=5*2 the result is “5*2″

Let myVar=5*2 the result is “10″

26) Explain QlikView Resident Load?

Create a new logical table in QlikView, based on a previously loaded (resident) table.

27) What is Apply Map (Mapping Tables)?

Sometimes you need to add an extra field to a table to use a combination of fields

from different tables, or you want to add a field to clean up the data structure. Qlik- View has an effective way to add single fields to a table called mapping tables. syntax — mapping ( load statement | select statement )

applymap( ‘mapname’, expr, [ , defaultexpr ] )

28) What is Dimensions ( What is difference between Expression and Dimension)?

Each data warehouse consists of dimensions and measures. Dimensions allow data analysis from various perspectives. For example, time dimension could show you the breakdown of sales by year, quarter, month, day and hour. Product dimension could help you see which products bring in the most revenue. Supplier dimension could help you choose those business partners who always deliver their goods on time. Customer dimension could help you pick the strategic set of consumers to whom you’d like to extend your very special offers.

29) Explain about Normalized Data?

Well Structured Form of Data, which doesnt have any repetition or redundancy of data. Its a kind of Relational data. Its mainly used in OLTP kind of stuffs Denormalized Data – Its a whole bunch of data without any relationship among themselves, with redundancy of data. Its mainly used in OLAP kind of stuffs.

30) What Is Star Sechma ?

A star schema is the simplest form of dimensional model, in which data is organized into facts and dimensions. A fact is an event that is counted or measured, such as a sale or login. A dimension contains reference information about the fact, such as date, product, or customer. A star schema is diagramed by surrounding each fact table with its associated dimensions table. The output diagram resembles a star.

Star Schema Definition : A means of aggregating data based on a set of known dimensions. It stores data multidimensionality in a two dimensional Relational Database Management System (RDBMS), such as Oracle.

31) What is Snowflaking Schema ?

Snowflake Schema: An extension of the star schema by means of applying additional dimensions to the Dimensions of a star schema in a relational environment. Snowflaking is a form of dimensional modeling; dimensions are stored in multiple relational dimension tables. A snowflake schema is a variation of the star schema. Snowflaking is used to improve the performance of specific queries. The schema is diagramed with each fact surrounded by its associated dimensions as in a star schema, and those dimensions are further related to other dimensions, branching out into a snowflake pattern.

32) What is Central Link Table?

In the event of multiple fact tables QlikView In-Memory Technology allows us to create a central link table that only contains the existing data combinations. Instead of Joining the tables the event dimensions can be merged (CONCATENATED) in to one central Link table. This link table can then be linked back to the event measures one side and the dimension tables on the other.

33) What is binary load ?

Binary load is loading data from another QV file. For example, you have application A.qvw. You can create another application B.qvw with script binary A.qvw. binary file where:

file ::= [ path ] filename

Examples:

Binary customer.qvw;

Binary c:\qv\customer.qvw;

The path is the path to the file, either absolute, or relative to the .qvw file containing this script line.

34) What is Container ?

A container object can be used to hold multiple charts. You can use a container object to put multiple charts in the same box. All charts will appear in the same window but only one chart will appear active at a given time. You can click the chart title to switch or toggle between charts. A word of advice: Use containers with caution. They form linked objects and might affect the properties of all linked objects.