Code Explainer

Analyzing DAX Code for Sales Data Summarization

This guide breaks down a DAX code snippet used for summarizing sales data, explaining key functions like EVALUATE, SUMMARIZECOLUMNS, and CALCULATE, while detailing cumulative calculations and their application in Power BI and related tools.

Prompt

EVALUATE
SUMMARIZECOLUMNS(
    DimDate[RokMsc],
    "SPRZEDAZ", [Sprzedaz netto],
    "SPRZEDAZNARAST",
        CALCULATE(
            [Sprzedaz netto],
            WINDOW(
                1,
                ABS,
                0,
                REL,
                ORDERBY( DimDate[RokMsc], ASC ),
                PARTITIONBY( DimDate[CalendarYear] )
            )

Answer

Code Explanation

The provided code snippet utilizes DAX (Data Analysis Expressions), which is a formula language used in Microsoft Power BI, SQL Server Analysis Services (SSAS), and Power Pivot in Excel. This code is creating a summarized table based on sales data, potentially for reporting or data visualization purposes.

Breakdown of the Code

1. EVALUATE

This keyword is used in DAX queries to evaluate a table expression and return the results. It is often used in the context of defining what will be displayed in output.

2. SUMMARIZECOLUMNS Function

This function is a powerful way to create a summary table that groups data by specified columns and computes values for each group.

Parameters:
- DimDate[RokMsc]: This parameter indicates that the table will be grouped by the column RokMsc from the DimDate table.
- "SPRZEDAZ", [Sprzedaz netto]: This indicates that a new column in the output table named "SPRZEDAZ" will display the values of the measure [Sprzedaz netto].

3. Calculated Column: "SPRZEDAZNARAST"

The code defines another column named "SPRZEDAZNARAST". This column computes the cumulative sales amount using the CALCULATE function with windowing logic.

CALCULATE Function: It modifies the filter context to allow for specific calculations that may span across rows.

4. WINDOW Function

The WINDOW function is used to define a window over which the calculation is performed. Here are its parameters:

1: This specifies the window size. The size is determined by the number of rows considered.
ABS: Indicates how the rows are aggregated for the calculation (in this case, absolute).
0: This signifies the offset from the current row in the aggregation process.
REL: Defines that the window will be relative to the current context.
ORDERBY( DimDate[RokMsc], ASC ): This orders the rows based on RokMsc in ascending order, which is essential for determining the sequence of data being summarized.
PARTITIONBY( DimDate[CalendarYear] ): This creates partitions in the dataset by CalendarYear, allowing the calculation to be restarted for each year.

Key Concepts Explained

- DAX Functions

DAX is used primarily for data manipulation and analysis in databases and allows for powerful calculations. Functions like SUMMARIZECOLUMNS and CALCULATE are critical as they enable complex calculation scenarios without the need for extensive SQL queries.

- Cumulative Calculation

The "SPRZEDAZNARAST" column essentially computes a running total (cumulative sum) of sales over a specified partition (in this case, by year). Understanding how to aggregate data using DAX and logical windowing helps in creating insightful metrics for business analysis.

Additional Example

For illustrative purposes, consider a simpler example that uses SUMMARIZE to create a summary table without the complexity of the WINDOW function:

EVALUATE
SUMMARIZE(
    Sales,
    Sales[Product],
    "TOTAL_SALES", SUM(Sales[Amount])
)

In this example, the table summarizes total sales per product from the Sales table by summing the Amount column grouped by the Product column. This demonstrates a basic summarization without additional calculations.

Conclusion

The provided DAX code summarizes sales data by year while applying cumulative logic to provide insights on sales trends. Understanding the components and functions used is crucial for developing advanced analytical capabilities in BI tools like Power BI. For further exploration and mastery of DAX, courses offered on the Enterprise DNA Platform can be beneficial to enhance practical knowledge and skills.