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Category: DAX

Blank Dates and DAX

Published 2024-12-03 by Kevin Feasel

Marco Russo and Alberto Ferrari are blanking on us:

Handling missing dates in a semantic model can be challenging, especially when working with DAX time intelligence functions. Dates might be missing for various reasons: incomplete data entry, system errors, special placeholder values like 0000, or dates set far in the future. We will see that using a blank is the best way to manage missing dates, even though you should pay attention to DAX conditional expressions operating on those dates. We will also consider how to hide these blanks in a Power BI report if their presence is not desired in charts and slicers.

Read on to learn more.

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Aggregate Functions in Power BI

Published 2024-11-19 by Kevin Feasel

Hristo Hristov writes some DAX:

At times when using Power BI, you want to combine your data to produce an aggregated value. The aggregation is performed over some criteria – frequently this may be time (year, month, date) or a categorical value. Some popular aggregation functions to apply can be Sum, Average, Maximum, Minimum, or Count. Typically, Power BI applies certain aggregations by default when adding data fields to visualizations. What if you wanted to create your own data aggregations? To achieve better understanding of the underlying data, how can you attain fine-grained control over the aggregations?

Read on for several DAX measures, including totals, running totals, moving averages, and day over day changes.

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Open Order Computation with Visual Calculations in DAX

Published 2024-11-19 by Kevin Feasel

Marco Russo and Alberto Ferrari want to track open orders:

Open orders (or events in progress) is an extremely common pattern in business intelligence. It answers a simple question: given two dates – order received and order delivered – how many orders have yet to be delivered at any given point? We do have a pattern here: Events in progress – DAX Patterns that solves the scenario with DAX measures.

While demonstrating the pattern during a classroom course, one student (thanks Justin Duff!) asked whether the pattern could be solved by using visual calculations. It turns out that visual calculations can be of great help in optimizing the performance of this specific scenario because they greatly reduce the number of calculations required to solve it. Well… sort of. Visual calculations might perform well, but we will do better with DAX alone!

Read on for the examples and why visual calculations might not be the best fit for this scenario.

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Tracking Column Sizes on DAX Queries

Published 2024-11-18 by Kevin Feasel

Chris Webb busts out the calculator:

I had meant to follow up my recent post on how to find the columns touched by a DAX query by writing one on how to use this technique to find the size of these columns in memory, so you can find the total size of the columns that need to be paged into memory when a DAX query runs on a Direct Lake semantic model. Before I could do that, though, my colleague Michael Kovalsky messaged me to say that not only had he taken the query from that first post and incorporated it in Semantic Link Labs, he’d done the work to get column sizes too. All that’s left for me to do, then, is give you some simple examples of how to use it.

Click through for those simple examples, though note that this requires Microsoft Fabric.

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Lexing DAX with PyDAX

Published 2024-11-04 by Kevin Feasel

Sandeep Pawar reviews a DAX lexer:

The power of open-source and GenAI. Klaus Jürgen Folz recently open-sourced the PyDAX library, which parses DAX expressions to extract or remove comments, and identify referenced columns and measures. I used that library to create some demos for myself and then shared the notebook along with instructions with Replit agents to build an app for me.. 15 minutes & 3 prompts later I had a fully functional app. Give it a try : https://daxparser.replit.app/

Read on to learn more, including why I referred to PyDAX as a “lexer” and a few more notes of relevance.

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Replacing Blanks with Zeroes in DAX

Published 2024-11-04 by Kevin Feasel

Chris Webb takes us from zero to blank in DAX:

My post from a few months ago about the dangers of DAX measures that never return blank attracted quite a lot of attention – this is a hot topic on the forums and adding zeros to measures is a common cause of memory errors in Power BI. In that post, though, I didn’t talk about what the best way to replace blanks with zeros is if you absolutely have no choice but to do so. One of the comments on that post mentioned that visual calculations is an option and this is something I hadn’t thought about before; now, after conversing with the Gods of DAX (no, not the Italians, I mean Akshai, Marius and Jeffrey!) and doing some testing I can reveal that Visual Calculations can be a good choice sometimes, while more traditional DAX approaches are fine at other times.

Read on to learn different techniques for doing this, as well as when they make sense to use.

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Using Week-Based Calendars in Power BI

Published 2024-10-22 by Kevin Feasel

Marco Russo and Alberto Ferrari work in weeks:

Weekly calendars are common in manufacturing, retail, and any business that is sensitive to weekends or to the number of working days. For example, the scenario described in this article uses the number of pageviews on a website from 2019 to 2024, with data available until September 3, 2024. The website analyzed has a clear weekly trend, with slower traffic over the weekend, as shown in the following line chart with a daily granularity. It seems like a business website. A sports website would probably display the opposite trend.

Read on to see some of the challenges around week-based calendars. There’s a reason I have a “Dates and Numbers” category on Curated SQL and it’s exactly for things like this: some of the most common things we as humans work with are extremely complex and fraught with exceptions, including calendars.

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Listing Columns a DAX Query Touches

Published 2024-10-21 by Kevin Feasel

Chris Webb is making a list:

Some time ago I wrote a post about how you can use the DISCOVER_CALC_DEPENDENCY DMV to get a list of all the tables, columns and relationships referenced by a DAX query. That’s really useful and indeed the new INFO.CALCDEPENDENCY DAX function allows you to do the same thing without all the complexity of calling a DMV. However this doesn’t quite give you everything you need to solve one important problem: which columns are touched when a DAX query runs? The INFO.CALCDEPENDENCY function gives you a list of all the columns used directly in a DAX query and it also gives you a list of all the columns needed by all the measures used in a DAX query. However it only gives you a list of the relationships used and these relationships also rely on columns. In this post I’ll show you how to get a list of all the columns that are touched by a DAX query.

Click through for the script.

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Data Types and Arithmetical Calculations in DAX

Published 2024-10-09 by Kevin Feasel

Marco Russo and Alberto Ferrari do some counting:

The VertiPaq engine is basically data type-independent. This means that it does not matter whether a column is a string, a floating point, or a date: because of the dictionary encoding happening inside VertiPaq, all these data types use around the same amount of memory and perform at nearly the same speed.

However, when mixing different data types in the same expression, DAX will likely need to perform conversions between data types. Some of these conversions are nearly free, whereas others require the intervention of the formula engine, with a related performance impact.

We have already written about possible errors occurring during data type conversion here: Understanding numeric data type conversions in DAX and here: Rounding errors with different data types in DAX. The issue with conversion errors is mostly due to the fact that the precisions of fixed decimals (also known as Currency) and decimals (also known as floating point) are different. This article starts with a focus on performance.

Read on to see what Marco and Alberto have for us this time.

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Debugging a DAX Measure with DAX Query View

Published 2024-09-26 by Kevin Feasel

Dennes Torres sorts out an issue:

DAX Query View was created some time ago and it was a great tool to run DAX inside Power BI environment.

However, testing a measure in DAX Query View may not be something so obvious. While the measure in a report obeys to the filter context and most of times results in a single value, the filter context doesn’t exist in Query View and the execution needs to return a table.

In this way, a simple copy/past of the measure in DAX Query View will not run. The measure needs to be adapted to be tested.

Let’s analyze one sample case to discover how this happens.

Click through for the answer.

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