Histograms

Analyzing Business Data in SQL

Michel Semaan

Data Scientist

Histograms - overview

Histogram: Visualizes the frequencies of each value in a dataset

Frequency table

orders  users
------  -----
1       7
2       42
3       65
...     ...

Histogram of orders per user

Histograms - query (I)

WITH user_orders AS (
  SELECT
    user_id,
    COUNT(DISTINCT order_id) AS orders
  FROM meals
  JOIN orders ON meals.meal_id = orders.meal_id
  GROUP BY user_id)


SELECT
  orders,
  COUNT(DISTINCT user_id) AS users
FROM user_orders
GROUP BY orders
ORDER BY orders ASC;

Histograms - query (II)

WITH user_revenues AS (
  SELECT
    user_id,
    SUM(meal_price * order_quantity) AS revenue
  FROM meals
  JOIN orders ON meals.meal_id = orders.meal_id
  GROUP BY user_id)


SELECT
  ROUND(revenue :: NUMERIC, -2) AS revenue_100,
  COUNT(DISTINCT user_id) AS users
FROM user_revenues
GROUP BY revenue_100
ORDER BY revenue_100 ASC;