QlikView Interview Question and Answers-4

Question.1  Why and how QVDs are used ?

Answer:

  • It is faster to read data from a QVD file.
  • In QlikView script, data can be extracted from the table and stored in a QVD file.
  • Use multiple QVD files to create the efficient data model. Create dashboards by reading data from the QVD instead of data source.
  • QVD creation and data storage is done by using the STORE command. Unless a path is specified, generated QVD resides in the same folder as the qvw file.
  • Reading data from QVD is similar to reading from Table files such as xls or csv

Question.2  Name some of the functions used in creating a data model ?

Answer:

Functions or statements are used to get the required functionality. QlikView provides a
wide range of functions. Some of the functions used in scripts are

  • Load is used to load the data from the data source
  • Store is used to create and load data into QVD.
  • Mapping Load is used to create Mapping Table.
  • ApplyMap is used with Mapping load to map the expression or column to the table.
  • Peek is used to return the value of a field in a specific row in a table.
  • Autonumber is used to get distinct integer value of an expression. It can be used to convert concatenation of fields resulting in a string to an integer.
  • Concatenate appends the two tables. The resulting table will have a sum of the number of rows of table one plus the sum of the rows of the table two.
  • Year and Month are used to get Year and Month from a date.

Question.3  How two tables are joined in QlikView ?

Answer:

Two tables are joined by the use of the Join statement in the script. The join between the two tables is a single table containing the output of the join. Join can be inner, left, right or outer join.

Question.4  How Keep differs from a Join ?

Answer:

In QlikView, the result of a Join between 2 tables is one table containing the output of the join. Join between two tables is made based on the matching column.
Join and Keep have the same functionality except that join results in one table, whereas Keep contains two tables. It creates an output table, but also keeps the table which prefix keep by left or right.

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Question.5  What is concatenate? What is a similar database/SQL key word ?

Answer:

Concatenate or concatenation of tables in QlikView is similar to Union All in SQL.Concatenate appends the 2 tables and creates one table. The resulting column has the sum of columns of table 1 plus the sum of columns of table2.
Concatenate has 3 flavors

  • Automatic concatenation. When the number of columns and name of columns in the 2 tables are same, they are automatically concatenated.
  • Forced Concatenation. If number and the name of the columns are not same, force concatenation can be performed by using concatenate keyword between two tables.
  • NoConcatenate. To avoid the automatic concatenation use NoConcatenate key word between the tables.

Question.6  What is the difference between Join and concatenate?

Answer: 

  • Result of a join between two tables in one table.
  • In QlikView, Join can be defined as inner, outer, left and right. Join merges tables based on the join criteria or matching rows.
  • Unlike Join, Concatenate appends one table into another table.
  • Join adds columns and Concatenate add rows

Question.7  What is Resident load?

Answer:

Resident load is used to load fields from the already loaded table. Resident load is required, in case, some additional transformation or aggregation needs to be performed on the already loaded table/fields.

Question.8  What is preceding load in QlikView ?

Answer:

  • Preceding load allows you to perform multiple transformations in one load script.
  • Preceding load takes the input from the previous load statement.
  • Multiple load statements can be stacked one top of another, each performing a transformation by taking input from the previous load.
  • It also allows the use QlikView functions

Question.9  What is a Mapping table in QlikView ?

Answer:

It is always a good practice to keep the data model clean with less number of tables and links. If data model contains many lookup tables, you can remove them by using Mapping load. Mapping load creates Mapping table.

  • Mapping table in QlikView is implemented by prefixing load statement with Mapping.
  • Mapping table should contain only two columns. One is ID and other column used for mapping the value.
  • Use Apply Map function to switch the ID with the value.
  • Mapping table exists in a separate area in memory and are automatically deleted after script execution.

Question.10  How you will incorporate more than one fact table in QlikView ?

Answer:

If the data model contains more than one fact table, then these tables can be incorporated using Concatenate or Link tables.

Use Concatenate when the granularity of the tables are same. Use Link table when the granularity of the tables is different.

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