Obtains the number of rows that are currently available in the primary buffer.
RowCount ( )
Long. Returns the number of rows that are currently available, 0 if no rows are currently available, and -1 if an error occurs.
This expression in a computed field returns a warning if no data exists and the number of rows if there is data:
If(RowCount() = 0, "No Data", String(RowCount()))