FIRSTDATE Function (DAX)
Returns the first date in the current context for the specified column of dates.
To understand more about how context affects the results of formulas, see Context in DAX Formulas.
The dates argument can be any of the following:
A reference to a date/time column.
A table expression that returns a single column of date/time values,.
A Boolean expression that defines a single-column table of date/time values.
Constraints on Boolean expressions are described in the topic, CALCULATE Function (DAX).
When the current context is a single date, the date returned by the FIRSTDATE and LASTDATE functions will be equal.
Technically, the return value is a table that contains a single column and single value. Therefore, this function can be used as an argument to any function that requires a table in its arguments. Also, the returned value can be used whenever a date value is required.
The following sample formula creates a measure that obtains the first date when a sale was made in the Internet sales channel for the current context.
To see how this works, create a PivotTable and add the field CalendarYear to the Row Labels area of the PivotTable. Then add a measure, named FirstSaleDate, using the formula defined in the code section, to the Values area of the PivotTable.