## Mastering DAX and Power BI: A Technical Analysis

##### Description

In our course, we'll explore the intricate workings of DAX within Power BI, drilling down into its technical applications and examining how it leverages VertiPaq. Comparisons will be drawn to SQL, as well as possible calculation methods with LLMs, providing you with a complete understanding of this powerful data analysis tool. This course suits anyone with a foundational understanding of Power BI who wants to advance their knowledge of DAX’s architecture and capabilities.

The original prompt:

I want to learn more about how DAX actually works in Power BI. I want to understand the technical aspects of it and how it uses the vertipaq engine. How does this differ to SQL for example. Also how does it compare to how LLMs could calculate data.

# Lesson 1: Introduction to DAX

Welcome to the first lesson of our comprehensive course on Power BI’s data analysis expressions (DAX) language and its VertiPaq engine. Today, we will be focusing on an introduction to DAX, its functions, syntax, and potential use cases. With DAX being the heart of data modeling and analytics in Power BI, understanding its functions is essential in mastering this powerful tool.

## What is DAX?

Data Analysis Expressions (DAX) is a formula language used predominantly with Power Pivot, Power BI, and Analysis Services Tabular projects. DAX is designed to structure, summarize and analyze data, allowing users to create custom calculated fields and values in their data models.

## DAX Syntax

DAX syntax is relatively straightforward. It is based on an equation or expression that begins with an equal (=) sign, followed by the function, identifier, or constant value.

Here's a general structure of DAX syntax:

`= Function (Argument1, Argument2, …)`

For instance, if you want to calculate the sum of the sales, your DAX expression would look something like:

`= SUM ('SalesTable'[SalesAmount])`

In this expression, `SUM`

is the function, `'SalesTable'[SalesAmount]`

is the column reference.

## Basic DAX Functions

Understanding DAX entails familiarizing oneself with its most commonly used functions. Here are some examples:

**SUM**: Adds all the numbers in a column.**AVERAGE**: Calculates the average of a column.**MIN**: Returns the smallest number in a column.**MAX**: Returns the largest number in a column.**COUNT**: Counts the number of rows in a column.**CALCULATE**: One of the most powerful DAX functions, it allows you to change the context under which certain calculations are made.

## Real-Life Example

Here is a concrete example of a scenario where DAX can be used:

Let's say you have a business that sells office supplies and you manage a large data set in Power BI with columns for Item, OrderDate, and OrderAmount. You can create a calculated column to provide additional insights.

For instance, if you want to determine the total amount of sales for 'Pens' in the year 2022, your DAX expression would look something like this:

```
= CALCULATE(
SUM('Sales'[OrderAmount]),
'Sales'[Item] = "Pens",
YEAR('Sales'[OrderDate]) = 2022
)
```

In this expression, the `CALCULATE`

function changes the context in which the sum of the OrderAmount is evaluated - it's only summing the OrderAmount for rows where Item is 'Pens' and the OrderDate year is 2022.

And voila! With DAX, we’ve efficiently narrowed down the sale amount of a specific item in a specific year.

At the end of this course, you should be able to understand DAX expressions and surface valuable insights from your data in Power BI. However, keep in mind that DAX is a vast topic and it cannot be entirely covered in a single lesson.

In the upcoming lessons, we will be delving deeper into more complex DAX functions, DAX variables, creating measures vs calculated columns, Time intelligence in DAX, and much more.

# Understanding the Core Concepts of DAX: A Comprehensive Course Diving Deep into the Heart of Power BI's DAX Language

*DAX (Data Analysis Expressions)* is a computing language and programming construct that offers capabilities to create custom computations on data models in Power BI. Having already introduced the basics, we will move one step further and dive deep into the understanding of some core concepts of DAX.

## Section 1: How DAX Works

### The DAX Formula

A DAX formula is a construct that can be created in Power BI or related Microsoft applications. It is composed of:

- An
`=`

operator, which initiates the formula. - A
`function`

, which provides the computing capability. `Constants`

and`Identifiers`

, which represent numbers, text, or column references.- An
`operator`

for mathematical operations, comparative analysis, etc. `Comments`

for providing clarity or explaining the purpose of the formula.

Here is an example of a DAX formula:

```
=
SUMX(
'SalesTable',
'SalesTable'[Unit Price] * 'SalesTable'[Quantity]
)
```

### Functions and Operators

Every DAX formula uses one or more functions, with some common ones including COUNT, SUM, MIN, MAX, and AVERAGE. Beyond these, there are specific Text and Date functions available as well.

Additionally, DAX supports various operators, including both arithmetic (like `+`

, `-`

, `*`

, `/`

) and comparison operators (like `=`

, `>`

, `<`

, `>=`

, `<=`

, `<>`

).

### Contexts

There are two types of contexts:

`Row context`

: in a DAX formula, it refers to the specific row of the table being evaluated currently.`Filter context`

: this restricts the set of data that is available for formulas. The filter comes into play when user actions, report interactions, or DAX functions narrow down the data that is visible to different calculations.

Understanding the interaction between these two contexts is fundamental to effectively using DAX.

## Section 2: DAX Table Functions

Table functions return a table and are typically used in the `filter`

argument of the CALCULATE function.

Example of a DAX formula using table functions:

```
=
CALCULATE (
SUM ('SalesTable'[Sales Amount]),
FILTER (
'SalesTable',
'SalesTable'[Sales Amount] > 1000
)
)
```

In this case, the FILTER is creating a new table where each row has a 'Sales Amount' greater than 1000. This example indicates the power of DAX to manipulate tabular data inside its computations.

## Section 3: Evaluation Context & Context Transition

Evaluation context refers to the environment in which DAX formulas are computed. This encompasses both the row context and any filter context that exists. Understanding this can help debug and optimize DAX expressions.

`Context transition`

refers to the transformation of the row context into an equivalent filter context, usually occurring during a CALCULATE or CALCULATETABLE function.

## Section 4: DAX Iterators

Iterators are powerful DAX concept that allow iterating through a table - row by row. Functions such as SUMX, COUNTX, MINX, MAXX, and AVERAGEX are examples of iterators.

Here is an example of DAX iterator:

```
=
SUMX (
'SalesTable',
'SalesTable'[Quantity] * 'SalesTable'[Unit Price]
)
```

The SUMX function here is iterating over each row of the 'SalesTable' table and performing the multiplication operation for each row. Then, it takes the sum of these results.

## Wrapping Up

The core concepts discussed, provide a foundational understanding of the DAX language. However, to truly master DAX, one needs to practice these concepts across various data models and gain hands-on experience. With proficiency in DAX, comes the ability to extract substantial insights from data in Power BI!

# Lesson 3: Diving Deeper Into DAX Functions

After building a solid foundational understanding of DAX concepts, we're going to dive deeper into DAX functions. In this lesson, we'll explore some of the most frequently used functions in DAX and how they work. We'll also explain how to use these functions to extract insights from data in Power BI.

## Table of Contents

- Aggregation Functions
- Time Intelligence Functions
- Filter Functions
- Text & Data Type Functions
- Relationship Functions

## 1. Aggregation Functions

Aggregation functions provide a way to compute summary statistics over a specified data set. These functions are useful when you need to provide summaries or trends of data in your dataset.

A common aggregation function is `SUM`

, which returns the sum of a column. It's used when the requirement is to calculate total sales, total quantity sold, or total salary, etc.

Syntax: `SUM(<column>)`

Example: `SUM([Sales Amount])`

Another common aggregation function is `COUNT`

, which returns the count of rows in a column. It's used when the requirement is to calculate the number of rows that meet specified criteria, like counting the number of units sold.

Syntax: `COUNT(<column>)`

Example: `COUNT([Order ID])`

## 2. Time Intelligence Functions

In business reporting, time is a critical factor. Time intelligence functions help us perform time and date-based calculations. These functions allow you to build charts that show trends over time.

A couple of important Time Intelligence Functions are `CALENDAR`

and `YEAR`

.

The `CALENDAR`

function returns a table with one column of all dates between two provided dates.

Syntax: `CALENDAR(<start_date>, <end_date>)`

Example: `CALENDAR(DATE(2020, 1, 1), DATE(2020, 12, 31))`

will result in a Date table for the year 2020.

The `YEAR`

function returns the year of the specified date, which can help when we want to group sales data year-wise or month-wise.

Syntax: `YEAR(<date>)`

Example: `YEAR([Transaction Date])`

## 3. Filter Functions

Filter functions are used to filter out data that matches certain conditions. These are essential when creating measures that are tailored to fit specified criteria.

The `FILTER`

function is one of these, returning a table that has been filtered.

Syntax:`FILTER(<table>, <filter_expression>)`

Example: `FILTER(Sales, [Sales Amount] > 10000)`

will return all the rows from the Sales table where the Sales Amount is greater than 10000.

## 4. Text & Data Type Functions

Text, data type conversion functionality is an integral part of DAX.

`CONCATENATE`

is a commonly used function which combines two text strings into one text string.

Syntax: `CONCATENATE(<text1>, <text2>)`

Example: `CONCATENATE([First Name], [Last Name])`

The `VALUE`

function converts a text string that represents a number to a number.

Syntax: `VALUE(<text>)`

Example: `VALUE("12345")`

## 5. Relationship Functions

The ability to use and manipulate relationships between tables is one of DAX's powerful features. Functions such as `RELATED`

allow you to access data from related tables.

`RELATED`

is used in a column expression for a calculated column to create a new row context by following a many-to-one relationship from the current table to a related table.

Syntax: `RELATED(<columnName>)`

Example: Suppose you have a Products table and a Sales table. If you want to create a new calculated column in the Sales table to show the product Name for each sale, you can use RELATED function - `RELATED(Products[Product Name])`

.

We've just scratched the surface of DAX functions in this chapter. Each function has its own syntax and uses, and learning them provides you with a powerful toolset to perform complex data manipulation and analysis activities. In the next chapters, we will dive deeper into some of these functions and explore real-world scenarios where they can be used to extract insights. Keep practicing these functions until you feel comfortable with them.

# Lesson 4: In-depth Understanding of Power BI’s VertiPaq Engine

## Introduction

In this lesson, we will dive deep into the VertiPaq engine of Power BI. This engine forms the core of Power BI and is responsible for storing and retrieving data efficiently. It's crucial to grasp how VertiPaq works in order to design high-performance BI solutions.

## Understanding The VertiPaq Engine

The VertiPaq engine, also known as the xVelocity in-memory analytics engine, acts as the primary data storage and query processing component within Power BI. This columnar database technology aims to deliver fast performance for handling large data volumes involving complex calculations.

An essential feature of the VertiPaq engine is that it compresses data and stores it in a column-wise manner. This feature is key to its high speed and efficiency since it allows more data to be stored in the memory, facilitating rapid analysis and computations.

Consider an example, if you were asked to find the sum of sales in a data table, a row-based engine would have to scan each row and then each column within those rows to locate and sum the sales data. Conversely, the VertiPaq engine simplifies this process by directly accessing the 'Sales' column, saving valuable resources and time.

## VertiPaq Compression Techniques

Various techniques are used by the VertiPaq engine to achieve high compression ratios.

**Value Encoding:**This form of encoding is used for columns that have integer values. It uses fewer bits to represent common values in the column, thereby reducing its memory footprint.**Hash Encoding:**This method is used for columns that contain non-integer values. With Hash encoding, each distinct value is assigned a unique hash and stored in a dictionary. The column then stores only references to those dictionary entries.**Run-Length Encoding (RLE):**RLE technique is used when the column data have a repeating pattern. It stores the repeating values, the starting position, and the length of the run.

## Segmentation

Another important concept in the VertiPaq engine is Segmentation. Data tables in VertiPaq are broken into segments of around 1 million rows. Each segment contains its individual dictionary for compression, contributing to the high compression ratio. This segmentation helps to optimize parallel operations when reading and scanning data.

For instance, querying a large table of customer orders might be heavy-duty for a conventional database engine. However, VertiPaq divides this task among several processors, each working on a different segment simultaneously, which significantly accelerates the query process.

## VertiPaq And DAX Relationship

While VertiPaq handles the storage and retrieval of data, Data Analysis Expressions (DAX) deals with the computation and analysis of this data. VertiPaq's data-optimized storage approach enables DAX to perform computations more efficiently. Therefore, understanding how VertiPaq operates can help you write better and more efficient DAX queries.

## Using VertiPaq Analyzer

VertiPaq Analyzer is a powerful tool which you can use to assess the performance of your Power BI data models. By analyzing your data model, VertiPaq Analyzer can provide insights about the overall memory footprint, giving you the opportunity to find optimization options of your BI system.

## Summary

In conclusion, the VertiPaq engine, with its unique columnar database structure and advanced compression techniques, enables fast and effective data analysis. By understanding how VertiPaq stores and retrieves data, you can develop improved DAX expressions, optimize your data model, and design more efficient Power BI solutions. In following lessons, we will explore how to use this knowledge in practice, by building and optimizing complex data models with issues of large volumes or the need for complex analytical computations.

# Lesson 5: DAX and VertiPaq: A Technical Relationship

In this lesson, you will learn about the technical relationship between the Data Analysis Expressions (DAX) language and the VertiPaq engine, which form the core of Microsoft's Power BI tool. Below, we comprehensively cover the nitty-gritty of their interfaces, and how these two vital components communicate with each other to optimize data retrieval and perform quick calculations.

## VertiPaq - DAX Interactions

VertiPaq and DAX work together to deliver the transformative analytics we desire in Power BI reports. VertiPaq handles the data storage and retrieval aspect providing columnstore indexing that leads to substantial storage compressions and loading performance. On the other hand, DAX serves as the calculation engine, delivering sophisticated logical analysis and real-time calculations you need for actionable insights.

The diagram above is a simple representation of how the two function together. The user interacts with the DAX querying language, which sends instructions to the VertiPaq storage engine. VertiPaq processes these requests by accessing and retrieving the necessary data, and the DAX calculation engine then processes this data to deliver the final result.

## QUERY vs FORMULA Engine Ambiguity

DAX language has evolved since its early days, and thus has left some ambiguity about its exact working - whether it works as a QUERY engine or a FORMULA engine. Indeed, DAX interfaces with VertiPaq as both, but playing two very distinct roles each time.

With Power BI, DAX primarily functions as a formula engine, transforming raw information inputs into actionable insights. DAX, in this case, sends formula instructions to VertiPaq, which then fetches the required data. The retrieved data is then sent back to DAX for final processing and presentation.

When you write a DAX query in Power BI, DAX's role reverses: it communicates the queries directly to VertiPaq. After processing the query, VertiPaq retrieves the data and sends it back to DAX, which then presents the data in the requested manner to the user.

## Interactions During a Query

Let us take a look at the interactions between DAX and VertiPaq for a specific user query, which will help understand the relationship.

### User Query

Let’s say a user inputs the following query:

```
EVALUATE
CALCULATETABLE ( 'Product',
'Product'[Price] > 100,
'Product'[Stock] > 0
)
```

The user wants to see a list of expensive in-stock products.

### DAX-VertiPaq Interaction

- The DAX parser checks for any syntax errors. Once the syntax is confirmed valid, the parser converts your query into an internal data structure called a query plan.
- The query plan is passed to the formula engine, which begins to vacuum up data into VertiPaq.
- VertiPaq can now filter the rows using the binary search algorithm for each condition and passes the results back to the DAX formula engine.
- The formula engine processes the returned rowset from VertiPaq and forms a tabular result, ready to serve to the end-user.

This demonstrates the sequence of the communications that occur between DAX and VertiPaq during a DAX query. The interaction is quite seamless, and it allows for quick data calculations and retrieval, which are critical in mitigating significant hurdles involving large data set analysis.

## Key Takeaways

Therefore, we see how the technical relationship between DAX and VertiPaq works to the advantage of the Power BI user. DAX provides the user-friendly language, simplifying the interaction with the data models. Simultaneously, VertiPaq focuses on the data storage and retrieval, providing a lightning-fast, efficient interaction with the DAX formula and query engines.

It's good to note how the interoperability of VertiPaq and DAX enhances the Average Joe's analytical prowess through Power BI: a testament to the phenomenal work Microsoft has done. Understanding how they interact helps better optimize DAX calculations and overall report performance.

In the next lesson, we will take a closer look at the VertiPaq optimization techniques and how to utilize these in DAX to make your Power BI reports run faster and more efficiently.

# Comparing DAX with SQL: Key Differences and Similarities

This lesson #6 will explore two key languages used in data analysis, SQL (Structured Query Language) and DAX (Data Analysis Expressions), making a comprehensive comparison of their key differences and similarities.

## Structure and Usage

### SQL

SQL is a scripting language that is used for managing and manipulating relational databases. It incorporates procedural and declarative paradigms of programming. SQL supports different kinds of operations such as selection, projection, joins, union, and other operations.

Example - Retrieve the names of employees earning more than $50,000:

```
SELECT
EmployeeName
FROM
Employees
WHERE
Salary > 50000;
```

### DAX

DAX, in comparison, is a functional language primarily used with Power BI, Analysis Services, and Power Pivot in Excel to analyze and perform calculations on data in tables and columns in those platforms.

Example - Retrieve the total salary paid per department:

```
Total Salary By Department =
SUMMARIZE (
Employees,
Employees[Department],
"Total Salary", SUM ( Employees[Salary] )
)
```

## Key Differences

**Data Handling**: SQL is used to handle data in a relational database model where data is stored in rows and columns. DAX, on the other hand, primarily operates on data in a tabular model where data is stored in tables and columns.**Usage Context**: SQL is used to extract and manipulate data in databases, whereas DAX is used to create new information from data already in the model such as creating new measures or calculated columns.**Calculation Characteristics**: DAX formulas include functions, operators, and values to perform dynamic calculations, while SQL is used to write queries to fetch data directly from the databases.**Learning Curve**: SQL is easier to learn, with widespread adoption and larger community support. DAX, being more niche and applied exclusively to certain Microsoft products, has a steeper learning curve.

## Key Similarities

**Data Analysis**: Both DAX and SQL serve as tools to extract and analyze data; they are just used in different environments and contexts.**Expression Type**: Both DAX and SQL utilise expressions. SQL uses expressions to fetch records from the database, DAX uses expressions to perform calculations on data stored in Power BI's models.**Categories of Functions**: They both categorize functions to facilitate a variety of data types: text, date/time, mathematical functions, etc.

## Conclusion

While SQL is a more general language used across a wide range of databases, DAX is a more specialized tool used specifically for Power BI, Analysis Services, and Power Pivot in Excel. Both have their strengths and preferred use cases. An understanding of both languages will allow you to better manipulate and analyze your data, regardless of where or how it is stored.

In the next lesson, we will explore common DAX functions, their syntax, and use cases in more depth. This will allow you to fully leverage the power of DAX in your data analysis. Let’s carry on with this journey into the heart of Power BI's data analysis.

# Lesson 7: Exploring Linear Layer Models (LLMs) Data Calculation Methodologies

Linear Layer Models (LLMs) are versatile and powerful data modeling techniques used in different realms of data analysis and predictive modeling, including the realm of Power BI's DAX language and VertiPaq engine. By understanding the methods used to calculate LLMs, you can leverage their power to create sophisticated analytical models.

## Understanding the Basics of LLMs

In the context of DAX and VertiPaq, LLMs are used to optimize the calculation of tabular functions and expressions. LLMs follow a simple equation - the sum of the product of each variable and their respective attribute, plus a constant. To understand how LLMs data calculation works, it's useful to first represent it symbolically:

LLM: Y = bX1 + cX2 + d… + a

Here Y is the dependent variable, X1, X2... are independent variables, and a, b, c... are coefficients.

## How LLMs Work in DAX

In DAX, LLMs are used to compress data while maintaining relationships between variables. They are heavily used in the VertiPaq engine to create efficient representations of complex data sets. All the relationships between variables are maintained in the metadata of the data structure, allowing DAX to perform calculations on the compressed data structure as if it were working with the original, uncompressed data.

Consider the following example:

You have a large data table, with millions of rows, that includes cities, sales, and dates. A linear layer model could be employed to compress this data into a smaller structure for efficiency, but without a loss of any consequential information.

## Calculation Methodologies of LLMs

Computation of an LLM, often involves the following steps:

### Step 1: Establish the Set of Variables

Defining the set of variables for the LLM equation is the first step. You'll include a dependent variable and a set of independent variables. This selection heavily depends on the business context and objectives of the analysis.

### Step 2: Calculate the Coefficients

The coefficients illustrate the influence each independent variable has on the dependent variable. In our sales data example, we would compute the coefficients that influence the operational outcome (sales generation).

These factors could be calculated using the methods like Ordinary Least Squares (OLS) or other fitting techniques. In DAX and VertiPaq, these calculations are achieved in the engine's internals once the data model is set up.

### Step 3: Validation and Interpretation

Once the LLM has been calculated, it's important to validate the output to ensure it makes sense in the context of your original data set and business objectives. This might involve comparing the output of the LLM against actual data, checking for significant differences, or testing how well the model predicts outcomes based on a sample of your data.

In Power BI, we can use DAX to create calculated columns, define measures, and design analytical reports that help in validating and interpreting the model.

## Conclusion

Understanding LLMs and how they calculate data allows for not only a deeper understanding of Power Bi's VertiPaq Engine and DAX, but also a more sophisticated and efficient utilization of them to produce powerful computational models. Through efficient data compression and the optimized calculation of tabular functions and expressions, LLMs bring a new level of agility and sophistication in handling large and complex data sets.

# Lesson 8: Effective Use of DAX and VertiPaq for Advanced Data Analysis

## Section 1: Recap

Before diving into the practical implementation of DAX and VertiPaq for advanced data analysis, let's recap the core concepts you've come to understand from the previous lessons. You should be familiar with DAX as a functional language used in Power BI to perform powerful data analysis, and VertiPaq as an in-memory columnar database engine optimizing data storage and retrieval for blazing performance. We have also discussed how DAX and VertiPaq work together and compared DAX with SQL.

We've also looked at LLMs (Lazy Materialized Views) data calculation methodologies, which offer a less resource-intensive approach for handling redundant computations or frequently utilized data. This knowledge forms a crucial foundation to this lesson, as discussed in our last lesson.

## Section 2: Advanced Use of DAX

Understanding and leveraging DAX capabilities fully in Power BI can transform raw data into insights. While DAX provides a range of time intelligence functions and filter contexts, it is essential to know how to tailor them to specific data analysis needs.

For instance, to analyze data across varying periods, we use a combination of CALCULATE, FILTER and ALLSELECTED DAX functions. Consider a real life scenario where sales managers want to compare yearly sales over different periods:

```
Sales Previous Year =
CALCULATE(
SUM('Sales'[Sales Amount]),
FILTER(
ALLSELECTED('Date'),
'Date'[Year] = MAX('Date'[Year])-1
)
)
```

In this example, the CALCULATE function changes the context in which the data is analyzed, the FILTER function restricts data in the table to a specific condition, and ALLSELECTED preserves the 'Date'[Year] filter context that is active outside the formula.

## Section 3: Leveraging VertiPaq for Optimized Data Storage and Calculation

VertiPaq engine operates behind the scenes of Power BI, greatly accelerating data retrieval and calculations. It identifies redundancies, compresses data, and executes operations in parallel across multiple cores.

These efficiencies are especially visible with large and complex data sets. To enhance the effectiveness of DAX formulas and ensure optimal performance, it's crucial to understand VertiPaq's metadata - tables, relationships, hierarchies, columns, data types and encoding.

One key principle is the columnar storage, where VertiPaq stores values of single columns in a compressed format. This optimized storage can greatly improve DAX calcuations such as:

`Total Sales = SUMX(Sales, Sales[Quantity]* Sales[Unit Price])`

Note the use of SUMX function, an iterator that works well with VertiPaq's columnar storage. It reduces the amount of data scanned to only the columns used in the SUMX function, enhancing calculation speed and efficiency.

## Section 4: Advanced Analysis using DAX and VertiPaq

Combining advanced DAX functions with VertiPaq optimizations can yield profound insights. For example, when evaluating the impact of changes in cost on profitability, we can introduce a what-if analysis.

First, create a what-if parameter in the 'Modeling' tab in the form of a slicer. Then, use this parameter within a DAX measure to show the projected impact:

`Project Profit = SUM(Sales[Sales Amount]) - (SUM(Sales[Quantity]) * [Cost Parameter])`

We can then use a visual to see the live impact of changes in costs on profitability, a powerful capability of DAX and VertiPaq.

This lesson has aimed to provide a practical understanding of effectively using VertiPaq and DAX for data analysis. The key is to understand the efficacy and strengths of DAX functions married with VertiPaq's storage and resource optimization to create dynamic, performant and insightful data analysis. Explore these functions and methodologies within your own context, and uncover the insights they can offer!