Advanced analysis using continuous aggregates and hyperfunctions

So far in this tutorial, you have ingested the data and run an aggregate query. Then you improved the performance of your analysis with continuous aggregates.

Now, let’s go over some ideas on analyzing the data using PostgreSQL and TimescaleDB, to help you understand more about player activity during the NFL season.

tip

Some of this analysis includes visualizations to help you see the potential uses of this data. These are created using the Matplotlib Python module, which is one of many great visualization tools.

Average yards run for a player over a game

This query uses a percentile approximation hyperfunction to find the mean yards run per game by a single player.

WITH sum_yards AS (
  SELECT a.player_id, displayname, SUM(yards) AS yards, gameid
  FROM player_yards_by_game a
  LEFT JOIN player p ON a.player_id = p.player_id
  GROUP BY a.player_id, displayname, gameid
)
SELECT player_id, displayname, mean(percentile_agg(yards)) as yards
FROM sum_yards
GROUP BY player_id, displayname
ORDER BY yards DESC

Your data should look like this:

When you run this query you might notice that the player_id and displayname are null for the first row. This row represents the average yard data for the football.

Average and median yards run per game by type of player

For this query, you use another one of the TimescaleDB percentile functions called percentile_agg. You can use the percentile_agg function to find the fiftieth percentile, which is the approximate median.

WITH sum_yards AS (
--Add position to the table to allow for grouping by it later
  SELECT a.player_id, displayname, SUM(yards) AS yards, p.position, gameid
  FROM player_yards_by_game a
  LEFT JOIN player p ON a.player_id = p.player_id
  GROUP BY a.player_id, displayname, p.position, gameid
)
--Find the mean and median for each position type
SELECT position, mean(percentile_agg(yards)) AS mean_yards, approx_percentile(0.5, percentile_agg(yards)) AS median_yards
FROM sum_yards
GROUP BY position
ORDER BY mean_yards DESC

If you scroll to the bottom of your results you should see this:

Notice how the Defensive End (DE) position has a large discrepancy between its mean and median values. The median data implies that most DE players do not run very much during passing plays. However, the mean data implies that some of the DE players must be running a significant amount.

Number of snap plays by player where they were on the offense

In this query, you are counting the number of passing events a player was involved in while playing offense. You might notice how much slower this query runs than the ones above which use continuous aggregates. The speed you see here is comparable to what you would get in the other queries without using continuous aggregates.

WITH snap_events AS (
-- Create a table that filters the play events to show only snap plays
-- and display the players team information
 SELECT DISTINCT player_id, t.event, t.gameid, t.playid,
  CASE
   WHEN t.team = 'away' THEN g.visitor_team
   WHEN t.team = 'home' THEN g.home_team
   ELSE NULL
   END AS team_name
 FROM tracking t
 LEFT JOIN game g ON t.gameid = g.game_id
 WHERE t.event LIKE '%snap%'
)
-- Count these events and filter results to only display data when the player was
-- on the offensive
SELECT a.player_id, pl.displayname, COUNT(a.event) AS play_count, a.team_name
FROM snap_events a
LEFT JOIN play p ON a.gameid = p.gameid AND a.playid = p.playid
LEFT JOIN player pl ON a.player_id = pl.player_id
WHERE a.team_name = p.possessionteam
GROUP BY a.player_id, pl.displayname, a.team_name
ORDER BY play_count DESC

Notice that the two highest passing plays are for Ben Roethlisberger and JuJu Smith-Schuster, a Quarterback and Wide Receiver, respectively, for the Pittsburgh Steelers.

Number of plays vs points scored

Use this query to get data on the number of plays and final score for each game during the 2018 season. This data is separated by team so that we can compare the number of plays with a team’s win or loss.

WITH play_count AS (
-- Count distinct plays, join on the stadium and game tables for team names and game date
    SELECT gameid, COUNT(playdescription) AS plays, p.possessionteam as team_name, g.game_date
    FROM play p
    LEFT JOIN game g ON p.gameid = g.game_id
    GROUP BY gameid, team_name, game_date
), visiting_games AS (
-- Join on scores to grab only the visting team's data
    SELECT gameid, plays, s.visitor_team as team_name, s.visitor_score AS team_score FROM play_count p
    INNER JOIN scores s ON p.team_name = s.visitor_team_abb
    AND p.game_date = s."date"
), home_games AS (
-- Join on scores to grab only the home team's data
    SELECT gameid, plays, s.home_team AS team_name , s.home_score AS team_score FROM play_count p
    INNER JOIN scores s ON p.team_name = s.home_team_abb
    AND p.game_date = s."date"
)
-- union the two resulting tables together
SELECT * FROM visiting_games
UNION ALL
SELECT * FROM home_games
ORDER BY gameid ASC, team_score DESC

This image is an example of a visualization that you could create with the results from this query. The scatter plot is grouped, showing the winning team’s plays and scores as gold, and the losing team’s plays and scores as brown.

The y-axis, or the number of plays for one team during a single game, shows that more passing plays do not always imply a guaranteed win. In fact, the top three teams with the highest number of plays for a single game all appeared to have lost. In football, this makes logical sense, as teams that are behind late in the game tend to pass more. There are many interesting facts which you could glean from this type of query, this scatter plot is just one possibility.

Average yards per game for top three players of each position

You can use this PostgreSQL query to extract the average yards run by an individual player over one game. This query only includes the top three highest players’ average yard values per position type. The data is ordered by the average yards run across all players for each position. This becomes important later on.

note

This query excludes some position types from the list due to such low average yard values, the excluded positions are Kicker, Punter, Nose Tackle, Long Snapper, and Defensive Tackle

WITH total_yards AS (
-- This table sums the yards a player runs over each game
 SELECT t.player_id, SUM(yards) AS yards, t.gameid
 FROM player_yards_by_game t
 GROUP BY t.player_id, t.gameid
), avg_yards AS (
-- This table takes the average of the yards run by each player and calls out thier position
 SELECT p.player_id, p.displayname, AVG(yards) AS avg_yards, p."position"
 FROM total_yards t
 LEFT JOIN player p ON t.player_id = p.player_id
 GROUP BY p.player_id, p.displayname, p."position"
), ranked_vals AS (
    -- This table ranks each player by the average yards they run per game
    SELECT a.*, RANK() OVER (PARTITION BY a."position" ORDER BY avg_yards DESC)
    FROM avg_yards AS a
), ranked_positions AS (
-- This table takes the average of the average yards run for each player so that we can order
-- the positions by this average of averages
    SELECT v."position", AVG(v.avg_yards) AS avg_yards_positions
    FROM ranked_vals v
    GROUP BY v."position"
)
SELECT v.*, p.avg_yards_positions FROM ranked_vals v
LEFT JOIN ranked_positions p ON v.position = p.position
WHERE v.rank <= 3 AND v.position != 'null' AND v.position NOT IN ('K', 'P', 'NT', 'LS', 'DT')
ORDER BY p.avg_yards_positions DESC, v.rank ASC

This is one possible visualization that you could create with this data:

Notice that the average yards overall for Free Safety players is higher than that of Wide Receivers (this is because of how we ordered the data, noted above). However, individual Wide Receivers run more yards on average per game. Also, notice that Kyle Juszczyk runs far more on average than other Fullback players.

It’s only halftime!

These example queries are just the beginning examples of the analysis you can perform on any time-series data with regular SQL and helpful features like continuous aggregates. Consider joining in stadium data that we provided to see if teams tend to score or run less at Mile High Stadium. Does natural or artificial turf affect any teams consistently?