Dax Function: FIRSTDATE
Category: Time Intelligence Functions
The FIRSTDATE function is a DAX (Data Analysis Expressions) function in Power BI. It returns the first date in the current filter context for a column containing date values. This function is often used in time intelligence calculations to find the start date of a specified period.
Purpose of the Function
The purpose of the FIRSTDATE function is to simplify calculations that require the earliest date in a given context. It is particularly useful for time-based calculations, reporting on specific periods, and creating dynamic visualizations.
Type of Calculations
- Start Date Identification: Extracts the first date from a dataset within a filter context.
- Time Intelligence Calculations: Works seamlessly with other DAX functions for date-based aggregations or comparisons.
- Dynamic Period Analysis: Determines the beginning of a filtered range for analysis.
Practical Use Cases
- Reporting Period Start Date: Identify the beginning date of a reporting period dynamically.
- First Transaction or Event Date: Calculate metrics starting from the first occurrence of an event.
- Custom Time Aggregations: Define start points for aggregations such as cumulative totals.
FIRSTDATE(<dates>)
| Parameter | Type | Description |
|---|---|---|
dates | Column | A column containing date values, usually from a date table, used to find the first date. |
How Does FIRSTDATE Dax Function Works?
- Evaluate Filter Context: The function considers the filter context of the
datescolumn. - Identify Year-End Date: Based on the calendar or fiscal year, it determines the final date of the year.
- Return Result: Outputs the determined year-end date.
For example:
- If the input column contains dates in 2025 and the
year_end_dateis left blank, the function will return December 31, 2025.
What Does It Return?
The function returns a single date value, which is the first date in the dates column based on the current filter context. If no dates exist in the filter context, it returns a blank value.
When Should We Use It?
- When calculating metrics that depend on the start of a specific period.
- For defining the initial date in custom date ranges.
- To create period-specific summaries, such as starting points for cumulative calculations.
Examples
Basic Usage
First Date = FIRSTDATE(Dates[Date])
Returns the earliest date in the Dates table based on the filter context.
Combining with Aggregations:
First Date Revenue = CALCULATE(
SUM(Sales[Revenue]),
FIRSTDATE(Dates[Date])
)
Calculates total revenue on the first date in the filter context.
Advanced Usage
First Date Last Year = CALCULATE(
FIRSTDATE(Dates[Date]),
DATEADD(Dates[Date], -1, YEAR)
)
Returns the first date from the previous year.
Tips and Tricks
- Use in Conjunction with CALCULATE: To filter data for the first date, wrap
FIRSTDATEwithin aCALCULATEfunction. - Ensure a Continuous Date Table: A complete date table ensures accurate results, especially in time intelligence calculations.
- Handle Blank Results Gracefully: Implement error handling or default values if the filter context might result in blank values.
Pitfalls:
- Sparse or incomplete date columns may lead to unexpected results.
- The function only works with valid date columns; ensure date formatting is correct.
Performance Impact of FIRSTDATE DAX Function:
- For large datasets, ensure optimized indexing on date columns to improve performance.
- Use the function with a dedicated date table for consistent results in time intelligence operations.
Related Functions You Might Need
LASTDATE: Returns the last date in the filter context.FIRSTNONBLANK: Returns the first non-blank value for a column.MIN: Returns the smallest value in a column or expression, including for dates.EARLIER: Refers to an earlier row context in calculated columns.
Want to Learn More?
For more information, check out the official Microsoft documentation for FIRSTDATE. You can also experiment with this function in your Power BI reports to explore its capabilities.
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It returns the earliest date in the current filter context from a specified date column.
No, it only works with valid date columns.
If no dates exist in the filter context, it returns a blank value.
While both can return the earliest date, FIRSTDATE considers the filter context, whereas MIN operates on the entire column or table.
Yes, but it needs to be combined with other DAX functions or a fiscal calendar for accurate results.
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