Running sums using window function SQL
A window function is like an aggregate function, except that it gives an output for every row in the dataset instead of a single row per group.
You can do aggregation along with window functions. A running sum using a window function is simpler than what is required using joins. The query duration can also be much faster.
A table called schedule
, having columns train_id
, station
, time
, and diff_min
is provided for you. The diff_min
column gives the elapsed time between the current station and the next station on the line.
This exercise is part of the course
Introduction to Spark SQL in Python
Exercise instructions
- Run a query that adds an additional column to the records in this dataset called
running_total
. The columnrunning_total
SUM()
s the difference between station time given by thediff_min
column. - Run the query and display the result.
Hands-on interactive exercise
Have a go at this exercise by completing this sample code.
# Add col running_total that sums diff_min col in each group
query = """
SELECT train_id, station, time, diff_min,
____(____) OVER (PARTITION BY ____ ORDER BY ____) AS running_total
FROM schedule
"""
# Run the query and display the result
spark.____(query).show()