ROW_NUMBER windowing function aggregate is how to assign row numbers.
ROW_NUMBER is part of Windowing Functions and that topic too complex for this tutorial. See the Windowing Functions documentation for details. However, for now we do want to show you the proper way to number rows in U-SQL using
ROW_NUMBER because it is a popular topic.
@rs1 = SELECT ROW_NUMBER() OVER ( ) AS RowNumber, Start, Region FROM @searchlog;