Similar to a left join, but different in distinct ways that allow you to do cool things in your QlikView scripts that would be difficult to do or would otherwise involve many steps. We will first look at the properties of these functions and examine the syntax. Then we will review 8 different applications of this to help you understand where these functions are a good fit. First, a mapping table must be created.
In my session on data modeling, I explain how you can Qlikview 11 with various types of Slowly Changing Dimensions in QlikView. One of the techniques I explain is using hash functions to detect changes in historical records.
During the previous events, this always lead to two questions from the audience: What exactly are hash functions and hashes?
And, from those who already know the answer to the first question: Today I will answer both questions and hopefully give you some insight into hash functions, their usefulness in QlikView and the risks of hash collisions.
Hash functions A hash function is an algorithm that maps data of arbitrary length to data of a fixed length. The value returned by a hash function is like a fingerprint of the input value, and is called a hash value or simply hash.
For example, all of the text above can be translated into the following MD5 hash: You will notice that this hash is much shorter than the original string used to generate it. Besides that, if only a single character in the text is changed this will lead to a completely different hash.
This property makes hash functions very useful to compare things, for example files, but also historical versions of a record. A hash function is deterministic, meaning that the same input value should always lead to the same hash value.
Besides that, a good hash function is also uniform, which means that each hash value should have the same probability of being picked.
The image at the top of this post illustrates a very simple hash function.
Each of the four input values is mapped to a unique output value. The number of bits determines the output range of the function. These functions basically take the output of the Hash and Hash function and passes it through the AutoNumber function.
While I think they have a nicer syntax than the regular AutoNumberyou can supply a comma-separated list of fields instead of a concatenated string, the usefulness of these functions eludes me. Detecting changed records Consider a QlikView application containing the following Employee table: Now, assume we get some new, changed data and want to quickly determine which rows have changed: As you can see, Jim has moved to another office.
How can we detect that this row has changed? We could compare each field in the table to each previous version of the field, but as we are only interested in detecting if the row has changed, using a hash function is a more elegant solution. Using Hash Name, Position, Office we can calculate a hash value for each row: This will be the topic of a future blog post.
Hash collisions As noted before, a hash function is an algorithm that maps data of arbitrary length to data of a fixed length. When different input values lead to the same output hash value, this is known as a hash collision.
Consider the following, simplified hash function: In this example, both Michael and Toby get the same hash value of 2.QlikView developers quickly find themselves in a mess of tables with circular references and synthetic keys galore.
Learn the difference between your fact tables and your dimensional tables. QlikView has been around since , but has only really taken off in recent years as a leader in the in-memory BI space and, more recently, in the data discovery area.
QlikView features the ability to consolidate relevant data from multiple sources. QlikView has been around since , but has only really taken off in recent years as a leader in the in-memory BI space and, more recently, in the data discovery area. QlikView features the ability to consolidate relevant data from multiple sources.
QlikView ist das Hauptprodukt des Softwareunternehmens QlikTech, das in Radnor, Pennsylvania seinen Hauptsitz hat. QlikView gehört zur Kategorie Business-Intelligence-Software..
QlikView ist ein Analyse- und Reporting-System. Die assoziative In-Memory-Suchtechnologie analysiert Daten und liefert dem Anwender Erkenntnisse und . Feb 03, · what I also forgot to mention is the fact that when I remove the last 2 fields in the group by line, and just say.
group by [Property Reference] ;. Qlikview is a business intelligence and analytic software, which improves the sense of your business data and improves your skill of making innovative business decisions. The latest version of Qlikview software available is Qlikview 11, many people may not know how to use this software but with the.