FIRSTDATE Function (DAX)
Returns the first date in the current context for the specified column of dates.
A column that contains dates.
A table containing a single column and single row with a date value.
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.